From 54351a5c75d8902d1d4c2eb2f6590bcf126348d4 Mon Sep 17 00:00:00 2001
From: Roman Leventov <leventov.ru@gmail.com>
Date: Tue, 6 Nov 2018 23:38:08 +0100
Subject: [PATCH] Fix various bugs; Enable more IntelliJ inspections and update
 error-prone (#6490)

* Fix various bugs; Enable more IntelliJ inspections and update error-prone

* Fix NPE

* Fix inspections

* Remove unused imports
---
 .idea/inspectionProfiles/Druid.xml            | 46 +++++++++++++++++--
 .../timecompare/TimeCompareBenchmark.java     | 32 +++++--------
 .../java/util/common/guava/Comparators.java   | 20 --------
 .../java/util/emitter/core/Emitters.java      |  2 +-
 .../client/pool/ChannelResourceFactory.java   |  2 +-
 .../org/apache/druid/math/expr/ExprEval.java  | 17 ++++++-
 .../collections/OrderedMergeIteratorTest.java | 11 ++---
 .../util/common/guava/ComparatorsTest.java    | 28 -----------
 .../util/common/guava/ConcatSequenceTest.java |  4 +-
 .../util/common/guava/SequenceTestHelper.java |  4 +-
 .../druid/extendedset/intset/BitIterator.java |  2 +-
 .../druid/extendedset/intset/ConciseSet.java  | 17 +++----
 .../intset/ImmutableConciseSet.java           |  2 +-
 .../druid/firehose/azure/AzureBlob.java       |  4 +-
 .../cassandra/CassandraDataSegmentPuller.java |  3 +-
 .../firehose/cloudfiles/CloudFilesBlob.java   |  6 +--
 .../CloudFilesStorageDruidModule.java         |  2 +-
 .../firehose/kafka/KafkaSimpleConsumer.java   |  4 +-
 .../MaterializedViewSupervisor.java           |  3 +-
 .../input/orc/OrcIndexGeneratorJobTest.java   |  4 +-
 .../DoublesSketchBuildAggregator.java         |  3 +-
 .../DoublesSketchBuildBufferAggregator.java   |  3 +-
 .../datasketches/theta/SketchHolder.java      |  1 +
 ...SketchToQuantilesSketchPostAggregator.java |  2 +-
 .../quantiles/GenerateTestData.java           |  3 +-
 .../DruidKerberosAuthenticationHandler.java   | 14 +++---
 .../kerberos/KerberosAuthenticator.java       |  2 +-
 .../hdfs/HdfsDataSegmentPusherTest.java       | 21 +++++----
 .../histogram/ApproximateHistogram.java       |  5 +-
 .../histogram/ApproximateHistogramTest.java   |  2 +
 .../kafka/supervisor/KafkaSupervisor.java     | 15 ++++--
 .../druid/indexing/kafka/test/TestBroker.java |  4 +-
 .../namespace/cache/CacheSchedulerTest.java   |  2 +-
 .../cache/JdbcExtractionNamespaceTest.java    |  4 +-
 .../protobuf/ProtobufInputRowParser.java      |  4 +-
 .../variance/VarianceGroupByQueryTest.java    | 20 ++++----
 .../variance/VarianceTimeseriesQueryTest.java | 17 +++----
 .../druid/hll/HyperLogLogCollector.java       |  6 +--
 .../hll/HyperLogLogCollectorBenchmark.java    |  1 +
 .../druid/indexer/IndexGeneratorJobTest.java  |  4 +-
 .../indexing/common/task/HadoopIndexTask.java |  2 +-
 .../overlord/hrtr/HttpRemoteTaskRunner.java   |  2 +-
 .../supervisor/SupervisorManager.java         |  2 +-
 .../indexing/worker/WorkerTaskManager.java    |  2 +-
 .../IngestSegmentFirehoseFactoryTest.java     |  5 +-
 .../indexing/test/TestDataSegmentKiller.java  |  7 +--
 .../indexing/test/TestDataSegmentPusher.java  |  5 --
 .../CoordinatorResourceTestClient.java        | 10 ++--
 .../druid/tests/hadoop/ITHadoopIndexTest.java |  2 +-
 .../AbstractITRealtimeIndexTaskTest.java      |  2 +-
 ...penderatorDriverRealtimeIndexTaskTest.java |  2 +-
 .../druid/tests/indexer/ITKafkaTest.java      |  7 ++-
 .../indexer/ITRealtimeIndexTaskTest.java      |  2 +-
 pom.xml                                       |  9 ++--
 .../druid/query/groupby/GroupByQuery.java     | 43 +++++++++++++----
 .../epinephelinae/BufferArrayGrouper.java     |  2 +-
 .../epinephelinae/BufferHashGrouper.java      |  1 +
 .../LimitedBufferHashGrouper.java             |  1 +
 .../epinephelinae/SpillingGrouper.java        |  2 +-
 .../query/ordering/StringComparators.java     |  4 +-
 .../query/scan/ScanQueryLimitRowIterator.java |  2 +-
 .../search/SearchQueryQueryToolChest.java     | 12 ++---
 .../select/SelectResultValueBuilder.java      |  3 +-
 .../AggregateTopNMetricFirstAlgorithm.java    |  2 +-
 .../query/topn/InvertedTopNMetricSpec.java    | 19 +-------
 .../org/apache/druid/segment/IndexIO.java     |  9 ----
 .../BlockLayoutColumnarLongsSerializer.java   |  2 +-
 .../apache/druid/segment/filter/Filters.java  |  2 +-
 .../druid/segment/filter/LikeFilter.java      |  2 +-
 .../aggregation/JavaScriptAggregatorTest.java |  2 +-
 .../query/select/SelectBinaryFnTest.java      |  3 --
 .../TimeBoundaryQueryRunnerTest.java          |  8 ----
 .../segment/SchemalessTestSimpleTest.java     |  2 +
 .../client/cache/BytesBoundedLinkedQueue.java | 23 ++++------
 .../druid/metadata/SQLMetadataConnector.java  |  2 +-
 .../EventReceiverFirehoseFactory.java         |  2 +-
 .../coordinator/ReplicationThrottler.java     |  2 +-
 .../coordinator/SegmentReplicantLookup.java   |  4 +-
 .../server/http/DatasourcesResource.java      |  6 +--
 .../druid/server/http/IntervalsResource.java  | 16 ++-----
 .../http/LookupCoordinatorResource.java       |  2 +-
 .../jetty/JettyServerInitUtils.java           |  2 +-
 .../PreResponseAuthorizationCheckFilter.java  |  7 ++-
 .../security/SecuritySanityCheckFilter.java   |  3 +-
 .../client/CachingClusteredClientTest.java    |  3 ++
 .../cache/BytesBoundedLinkedQueueTest.java    |  5 +-
 .../druid/client/cache/HybridCacheTest.java   |  4 +-
 .../client/cache/MemcachedCacheBenchmark.java |  2 +-
 .../appenderator/AppenderatorPlumberTest.java | 27 ++---------
 .../CuratorDruidCoordinatorTest.java          |  3 +-
 ...criptTieredBrokerSelectorStrategyTest.java |  1 -
 .../CoordinatorJettyServerInitializer.java    |  3 +-
 .../apache/druid/cli/PullDependencies.java    |  1 +
 .../cli/QueryJettyServerInitializer.java      |  3 +-
 .../druid/sql/avatica/DruidConnection.java    | 14 +-----
 95 files changed, 302 insertions(+), 359 deletions(-)

diff --git a/.idea/inspectionProfiles/Druid.xml b/.idea/inspectionProfiles/Druid.xml
index b1748e7c921..4ada21411dc 100644
--- a/.idea/inspectionProfiles/Druid.xml
+++ b/.idea/inspectionProfiles/Druid.xml
@@ -11,28 +11,35 @@
     <inspection_tool class="ArrayObjectsEquals" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ArraysAsListWithZeroOrOneArgument" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="AssertWithSideEffects" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="CapturingCleaner" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="CastConflictsWithInstanceof" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="CastToIncompatibleInterface" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="CatchMayIgnoreException" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="m_ignoreCatchBlocksWithComments" value="false" />
     </inspection_tool>
     <inspection_tool class="CheckValidXmlInScriptTagBody" enabled="true" level="WARNING" enabled_by_default="true" />
+    <inspection_tool class="ClassGetClass" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ClassNewInstance" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="CollectionAddedToSelf" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ComparableImplementedButEqualsNotOverridden" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="ComparatorMethodParameterNotUsed" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="ComparatorResultComparison" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="CompareToUsesNonFinalVariable" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ConstantAssertCondition" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="Contract" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="CopyConstructorMissesField" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="CovariantEquals" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="EmptyInitializer" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="EmptyStatementBody" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="m_reportEmptyBlocks" value="true" />
       <option name="commentsAreContent" value="true" />
     </inspection_tool>
+    <inspection_tool class="EndlessStream" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="EqualsAndHashcode" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="EqualsBetweenInconvertibleTypes" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="EqualsOnSuspiciousObject" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="EqualsUsesNonFinalVariable" enabled="true" level="WARNING" enabled_by_default="true" />
+    <inspection_tool class="EqualsWhichDoesntCheckParameterClass" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="EqualsWithItself" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="FieldCanBeLocal" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="EXCLUDE_ANNOS">
@@ -72,6 +79,17 @@
     <inspection_tool class="MathRandomCastToInt" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="MavenModelInspection" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="MismatchedArrayReadWrite" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="MismatchedCollectionQueryUpdate" enabled="true" level="ERROR" enabled_by_default="true">
+      <option name="queryNames">
+        <value />
+      </option>
+      <option name="updateNames">
+        <value />
+      </option>
+      <option name="ignoredClasses">
+        <value />
+      </option>
+    </inspection_tool>
     <inspection_tool class="MismatchedStringBuilderQueryUpdate" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="MissingOverrideAnnotation" enabled="true" level="WARNING" enabled_by_default="true">
       <scope name="NonGeneratedFiles" level="ERROR" enabled="true">
@@ -93,6 +111,7 @@
     </inspection_tool>
     <inspection_tool class="ObjectEqualsNull" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ObjectToString" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="OverwrittenKey" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="PrimitiveArrayArgumentToVariableArgMethod" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="RedundantThrows" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="RedundantTypeArguments" enabled="true" level="ERROR" enabled_by_default="true" />
@@ -182,22 +201,38 @@
         <constraint name="E" regexp="java\.lang\.UnsupportedOperationException" within="" contains="" />
         <constraint name="x" minCount="0" maxCount="2147483647" within="" contains="" />
       </searchConfiguration>
+      <searchConfiguration name="Use TypeReference&lt;List&lt;...&gt;&gt; instead" created="1539884261626" text="TypeReference&lt;ArrayList&lt;$E$&gt;&gt;" recursive="false" caseInsensitive="true" type="JAVA">
+        <constraint name="__context__" target="true" within="" contains="" />
+        <constraint name="E" within="" contains="" />
+      </searchConfiguration>
+      <searchConfiguration name="Use TypeReference&lt;Map&lt;...&gt;&gt; instead" created="1539884261626" text="TypeReference&lt;HashMap&lt;$K$, $V$&gt;&gt;" recursive="false" caseInsensitive="true" type="JAVA">
+        <constraint name="__context__" target="true" within="" contains="" />
+        <constraint name="K" within="" contains="" />
+        <constraint name="V" within="" contains="" />
+      </searchConfiguration>
+      <searchConfiguration name="Use TypeReference&lt;Set&lt;...&gt;&gt; instead" created="1539884261626" text="TypeReference&lt;HashSet&lt;$E$&gt;&gt;" recursive="false" caseInsensitive="true" type="JAVA">
+        <constraint name="__context__" target="true" within="" contains="" />
+        <constraint name="E" within="" contains="" />
+      </searchConfiguration>
     </inspection_tool>
     <inspection_tool class="SpellCheckingInspection" enabled="false" level="TYPO" enabled_by_default="false">
       <option name="processCode" value="true" />
       <option name="processLiterals" value="true" />
       <option name="processComments" value="true" />
     </inspection_tool>
-    <inspection_tool class="StaticCallOnSubclass" enabled="true" level="WARNING" enabled_by_default="true" />
-    <inspection_tool class="StaticFieldReferenceOnSubclass" enabled="true" level="WARNING" enabled_by_default="true" />
+    <inspection_tool class="StaticCallOnSubclass" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="StaticFieldReferenceOnSubclass" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="StringConcatenationInFormatCall" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="StringConcatenationInMessageFormatCall" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="StringConcatenationMissingWhitespace" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="StringEquality" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="StringEqualsCharSequence" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="StringTokenizerDelimiter" enabled="true" level="ERROR" enabled_by_default="true" />
-    <inspection_tool class="SubtractionInCompareTo" enabled="true" level="WARNING" enabled_by_default="true" />
+    <inspection_tool class="SubtractionInCompareTo" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="SuspiciousArrayCast" enabled="true" level="WARNING" enabled_by_default="true" />
+    <inspection_tool class="SuspiciousArrayMethodCall" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="SuspiciousIndentAfterControlStatement" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="SuspiciousListRemoveInLoop" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="SuspiciousMethodCalls" enabled="true" level="ERROR" enabled_by_default="true">
       <option name="REPORT_CONVERTIBLE_METHOD_CALLS" value="true" />
     </inspection_tool>
@@ -226,6 +261,11 @@
       <option name="ignoreInModuleStatements" value="true" />
     </inspection_tool>
     <inspection_tool class="UnnecessaryInterfaceModifier" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="UnusedAssignment" enabled="true" level="ERROR" enabled_by_default="true">
+      <option name="REPORT_PREFIX_EXPRESSIONS" value="true" />
+      <option name="REPORT_POSTFIX_EXPRESSIONS" value="true" />
+      <option name="REPORT_REDUNDANT_INITIALIZER" value="true" />
+    </inspection_tool>
     <inspection_tool class="UnusedCatchParameter" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="m_ignoreCatchBlocksWithComments" value="false" />
       <option name="m_ignoreTestCases" value="false" />
diff --git a/benchmarks/src/main/java/org/apache/druid/benchmark/query/timecompare/TimeCompareBenchmark.java b/benchmarks/src/main/java/org/apache/druid/benchmark/query/timecompare/TimeCompareBenchmark.java
index 63533a995a9..d719fe25ff8 100644
--- a/benchmarks/src/main/java/org/apache/druid/benchmark/query/timecompare/TimeCompareBenchmark.java
+++ b/benchmarks/src/main/java/org/apache/druid/benchmark/query/timecompare/TimeCompareBenchmark.java
@@ -95,7 +95,6 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
-import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ExecutorService;
@@ -167,15 +166,13 @@ public class TimeCompareBenchmark
     INDEX_MERGER_V9 = new IndexMergerV9(JSON_MAPPER, INDEX_IO, OffHeapMemorySegmentWriteOutMediumFactory.instance());
   }
 
-  private static final Map<String, Map<String, Object>> SCHEMA_QUERY_MAP = new LinkedHashMap<>();
-
   private void setupQueries()
   {
     // queries for the basic schema
-    Map<String, Object> basicQueries = new LinkedHashMap<>();
     BenchmarkSchemaInfo basicSchema = BenchmarkSchemas.SCHEMA_MAP.get("basic");
 
-    QuerySegmentSpec intervalSpec = new MultipleIntervalSegmentSpec(Collections.singletonList(basicSchema.getDataInterval()));
+    QuerySegmentSpec intervalSpec =
+        new MultipleIntervalSegmentSpec(Collections.singletonList(basicSchema.getDataInterval()));
 
     long startMillis = basicSchema.getDataInterval().getStartMillis();
     long endMillis = basicSchema.getDataInterval().getEndMillis();
@@ -204,9 +201,7 @@ public class TimeCompareBenchmark
       );
       queryAggs.add(
           new FilteredAggregatorFactory(
-              new LongSumAggregatorFactory(
-                  "_cmp_sumLongSequential", "sumLongSequential"
-              ),
+              new LongSumAggregatorFactory("_cmp_sumLongSequential", "sumLongSequential"),
               new IntervalDimFilter(
                   ColumnHolder.TIME_COLUMN_NAME,
                   Collections.singletonList(previous),
@@ -235,8 +230,6 @@ public class TimeCompareBenchmark
           new TopNQueryQueryToolChest(new TopNQueryConfig(), QueryBenchmarkUtil.NoopIntervalChunkingQueryRunnerDecorator()),
           QueryBenchmarkUtil.NOOP_QUERYWATCHER
       );
-
-      basicQueries.put("topNTimeCompare", queryBuilderA);
     }
     { // basic.timeseriesTimeCompare
       List<AggregatorFactory> queryAggs = new ArrayList<>();
@@ -265,24 +258,21 @@ public class TimeCompareBenchmark
           )
       );
 
-      Druids.TimeseriesQueryBuilder timeseriesQueryBuilder = Druids.newTimeseriesQueryBuilder()
-                                                                   .dataSource("blah")
-                                                                   .granularity(Granularities.ALL)
-                                                                   .intervals(intervalSpec)
-                                                                   .aggregators(queryAggs)
-                                                                   .descending(false);
+      Druids.TimeseriesQueryBuilder timeseriesQueryBuilder = Druids
+          .newTimeseriesQueryBuilder()
+          .dataSource("blah")
+          .granularity(Granularities.ALL)
+          .intervals(intervalSpec)
+          .aggregators(queryAggs)
+          .descending(false);
 
       timeseriesQuery = timeseriesQueryBuilder.build();
       timeseriesFactory = new TimeseriesQueryRunnerFactory(
-          new TimeseriesQueryQueryToolChest(
-              QueryBenchmarkUtil.NoopIntervalChunkingQueryRunnerDecorator()
-          ),
+          new TimeseriesQueryQueryToolChest(QueryBenchmarkUtil.NoopIntervalChunkingQueryRunnerDecorator()),
           new TimeseriesQueryEngine(),
           QueryBenchmarkUtil.NOOP_QUERYWATCHER
       );
     }
-
-    SCHEMA_QUERY_MAP.put("basic", basicQueries);
   }
 
 
diff --git a/core/src/main/java/org/apache/druid/java/util/common/guava/Comparators.java b/core/src/main/java/org/apache/druid/java/util/common/guava/Comparators.java
index 500d5046bf1..fec9879826a 100644
--- a/core/src/main/java/org/apache/druid/java/util/common/guava/Comparators.java
+++ b/core/src/main/java/org/apache/druid/java/util/common/guava/Comparators.java
@@ -59,26 +59,6 @@ public class Comparators
     return NATURAL_NULLS_FIRST;
   }
 
-  /**
-   * This is a "reverse" comparator.  Positive becomes negative, negative becomes positive and 0 (equal) stays the same.
-   * This was poorly named as "inverse" as it's not really inverting a true/false relationship
-   *
-   * @param baseComp
-   * @param <T>
-   * @return
-   */
-  public static <T> Comparator<T> inverse(final Comparator<T> baseComp)
-  {
-    return new Comparator<T>()
-    {
-      @Override
-      public int compare(T t, T t1)
-      {
-        return baseComp.compare(t1, t);
-      }
-    };
-  }
-
   /**
    * Use Guava Ordering.natural() instead
    *
diff --git a/core/src/main/java/org/apache/druid/java/util/emitter/core/Emitters.java b/core/src/main/java/org/apache/druid/java/util/emitter/core/Emitters.java
index b7b4423f186..00d424b88fc 100644
--- a/core/src/main/java/org/apache/druid/java/util/emitter/core/Emitters.java
+++ b/core/src/main/java/org/apache/druid/java/util/emitter/core/Emitters.java
@@ -50,7 +50,7 @@ public class Emitters
       Lifecycle lifecycle
   )
   {
-    Map<String, Object> jsonified = new HashMap<>();
+    Map<String, Object> jsonified;
     if (props.getProperty(LOG_EMITTER_PROP) != null) {
       jsonified = makeLoggingMap(props);
       jsonified.put("type", "logging");
diff --git a/core/src/main/java/org/apache/druid/java/util/http/client/pool/ChannelResourceFactory.java b/core/src/main/java/org/apache/druid/java/util/http/client/pool/ChannelResourceFactory.java
index b52b55d682e..9c7f4c7d0ae 100644
--- a/core/src/main/java/org/apache/druid/java/util/http/client/pool/ChannelResourceFactory.java
+++ b/core/src/main/java/org/apache/druid/java/util/http/client/pool/ChannelResourceFactory.java
@@ -77,7 +77,7 @@ public class ChannelResourceFactory implements ResourceFactory<String, ChannelFu
   public ChannelFuture generate(final String hostname)
   {
     log.debug("Generating: %s", hostname);
-    URL url = null;
+    URL url;
     try {
       url = new URL(hostname);
     }
diff --git a/core/src/main/java/org/apache/druid/math/expr/ExprEval.java b/core/src/main/java/org/apache/druid/math/expr/ExprEval.java
index 20982e6b0f9..60009122de1 100644
--- a/core/src/main/java/org/apache/druid/math/expr/ExprEval.java
+++ b/core/src/main/java/org/apache/druid/math/expr/ExprEval.java
@@ -52,6 +52,9 @@ public abstract class ExprEval<T>
 
   public static ExprEval of(@Nullable String stringValue)
   {
+    if (stringValue == null) {
+      return StringExprEval.OF_NULL;
+    }
     return new StringExprEval(stringValue);
   }
 
@@ -180,7 +183,11 @@ public abstract class ExprEval<T>
         case DOUBLE:
           return this;
         case LONG:
-          return ExprEval.of(value == null ? null : asLong());
+          if (value == null) {
+            return ExprEval.of(null);
+          } else {
+            return ExprEval.of(asLong());
+          }
         case STRING:
           return ExprEval.of(asString());
       }
@@ -218,7 +225,11 @@ public abstract class ExprEval<T>
     {
       switch (castTo) {
         case DOUBLE:
-          return ExprEval.of(value == null ? null : asDouble());
+          if (value == null) {
+            return ExprEval.of(null);
+          } else {
+            return ExprEval.of(asDouble());
+          }
         case LONG:
           return this;
         case STRING:
@@ -236,6 +247,8 @@ public abstract class ExprEval<T>
 
   private static class StringExprEval extends ExprEval<String>
   {
+    private static final StringExprEval OF_NULL = new StringExprEval(null);
+
     private Number numericVal;
 
     private StringExprEval(@Nullable String value)
diff --git a/core/src/test/java/org/apache/druid/collections/OrderedMergeIteratorTest.java b/core/src/test/java/org/apache/druid/collections/OrderedMergeIteratorTest.java
index c636e9d7d96..e58b83b4e1a 100644
--- a/core/src/test/java/org/apache/druid/collections/OrderedMergeIteratorTest.java
+++ b/core/src/test/java/org/apache/druid/collections/OrderedMergeIteratorTest.java
@@ -26,6 +26,7 @@ import org.junit.Test;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
@@ -170,10 +171,9 @@ public class OrderedMergeIteratorTest
   @Test(expected = NoSuchElementException.class)
   public void testNoElementInNext()
   {
-    final ArrayList<Iterator<Integer>> iterators = new ArrayList<>();
-    OrderedMergeIterator<Integer> iter = new OrderedMergeIterator<Integer>(
+    OrderedMergeIterator<Integer> iter = new OrderedMergeIterator<>(
         Ordering.natural(),
-        iterators.iterator()
+        Collections.emptyIterator()
     );
     iter.next();
   }
@@ -181,10 +181,9 @@ public class OrderedMergeIteratorTest
   @Test(expected = UnsupportedOperationException.class)
   public void testRemove()
   {
-    final ArrayList<Iterator<Integer>> iterators = new ArrayList<>();
-    OrderedMergeIterator<Integer> iter = new OrderedMergeIterator<Integer>(
+    OrderedMergeIterator<Integer> iter = new OrderedMergeIterator<>(
         Ordering.natural(),
-        iterators.iterator()
+        Collections.emptyIterator()
     );
     iter.remove();
   }
diff --git a/core/src/test/java/org/apache/druid/java/util/common/guava/ComparatorsTest.java b/core/src/test/java/org/apache/druid/java/util/common/guava/ComparatorsTest.java
index 61ab1e4577d..816e2d5a32a 100644
--- a/core/src/test/java/org/apache/druid/java/util/common/guava/ComparatorsTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/common/guava/ComparatorsTest.java
@@ -31,34 +31,6 @@ import java.util.Comparator;
  */
 public class ComparatorsTest
 {
-  @Test
-  public void testInverse()
-  {
-    Comparator<Integer> normal = Comparators.comparable();
-    Comparator<Integer> inverted = Comparators.inverse(normal);
-
-    Assert.assertEquals(-1, normal.compare(0, 1));
-    Assert.assertEquals(1, normal.compare(1, 0));
-    Assert.assertEquals(0, normal.compare(1, 1));
-    Assert.assertEquals(1, inverted.compare(0, 1));
-    Assert.assertEquals(-1, inverted.compare(1, 0));
-    Assert.assertEquals(0, inverted.compare(1, 1));
-  }
-
-  @Test
-  public void testInverseOverflow()
-  {
-    Comparator<Integer> invertedSimpleIntegerComparator = Comparators.inverse(new Comparator<Integer>()
-    {
-      @Override
-      public int compare(Integer o1, Integer o2)
-      {
-        return o1 - o2;
-      }
-    });
-    Assert.assertTrue(invertedSimpleIntegerComparator.compare(0, Integer.MIN_VALUE) < 0);
-  }
-
   @Test
   public void testIntervalsByStartThenEnd()
   {
diff --git a/core/src/test/java/org/apache/druid/java/util/common/guava/ConcatSequenceTest.java b/core/src/test/java/org/apache/druid/java/util/common/guava/ConcatSequenceTest.java
index 481d1d11c32..cf5cabe99a8 100644
--- a/core/src/test/java/org/apache/druid/java/util/common/guava/ConcatSequenceTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/common/guava/ConcatSequenceTest.java
@@ -138,7 +138,7 @@ public class ConcatSequenceTest
               public Integer accumulate(Integer accumulated, Integer in)
               {
                 Assert.assertEquals(accumulated, in);
-                return ++accumulated;
+                return accumulated + 1;
               }
             }
         ).intValue()
@@ -154,7 +154,7 @@ public class ConcatSequenceTest
           public Integer accumulate(Integer accumulated, Integer in)
           {
             Assert.assertEquals(accumulated, in);
-            return ++accumulated;
+            return accumulated + 1;
           }
         }
     );
diff --git a/core/src/test/java/org/apache/druid/java/util/common/guava/SequenceTestHelper.java b/core/src/test/java/org/apache/druid/java/util/common/guava/SequenceTestHelper.java
index e4450210ae2..52082e3c339 100644
--- a/core/src/test/java/org/apache/druid/java/util/common/guava/SequenceTestHelper.java
+++ b/core/src/test/java/org/apache/druid/java/util/common/guava/SequenceTestHelper.java
@@ -134,7 +134,7 @@ public class SequenceTestHelper
             @Override
             public Integer accumulate(Integer accumulated, Integer in)
             {
-              return ++accumulated;
+              return accumulated + 1;
             }
           }
       );
@@ -156,7 +156,7 @@ public class SequenceTestHelper
             @Override
             public Integer accumulate(Integer accumulated, Integer in)
             {
-              return ++accumulated;
+              return accumulated + 1;
             }
           }
       );
diff --git a/extendedset/src/main/java/org/apache/druid/extendedset/intset/BitIterator.java b/extendedset/src/main/java/org/apache/druid/extendedset/intset/BitIterator.java
index fb96e433031..e6d3c6ea6de 100644
--- a/extendedset/src/main/java/org/apache/druid/extendedset/intset/BitIterator.java
+++ b/extendedset/src/main/java/org/apache/druid/extendedset/intset/BitIterator.java
@@ -29,7 +29,7 @@ public final class BitIterator implements IntSet.IntIterator
   private boolean literalAndZeroFill;
   private int nextIndex = 0;
   private int nextOffset = 0;
-  private int next = -1;
+  private int next;
 
   BitIterator(ImmutableConciseSet immutableConciseSet)
   {
diff --git a/extendedset/src/main/java/org/apache/druid/extendedset/intset/ConciseSet.java b/extendedset/src/main/java/org/apache/druid/extendedset/intset/ConciseSet.java
index 782f5fcff9b..c944195de34 100755
--- a/extendedset/src/main/java/org/apache/druid/extendedset/intset/ConciseSet.java
+++ b/extendedset/src/main/java/org/apache/druid/extendedset/intset/ConciseSet.java
@@ -1272,9 +1272,9 @@ public class ConciseSet extends AbstractIntSet implements Serializable
     final ConciseSet other = convert(o);
 
     // the word at the end must be the same
-    int res = this.last - other.last;
+    int res = Integer.compare(this.last, other.last);
     if (res != 0) {
-      return res < 0 ? -1 : 1;
+      return res;
     }
 
     // scan words from MSB to LSB
@@ -1295,9 +1295,9 @@ public class ConciseSet extends AbstractIntSet implements Serializable
               return -1;
             }
             // compare two sequences of zeros
-            res = getSequenceCount(otherWord) - getSequenceCount(thisWord);
+            res = Integer.compare(getSequenceCount(otherWord), getSequenceCount(thisWord));
             if (res != 0) {
-              return res < 0 ? -1 : 1;
+              return res;
             }
           } else {
             if (isZeroSequence(otherWord)) {
@@ -1305,9 +1305,9 @@ public class ConciseSet extends AbstractIntSet implements Serializable
               return 1;
             }
             // compare two sequences of ones
-            res = getSequenceCount(thisWord) - getSequenceCount(otherWord);
+            res = Integer.compare(getSequenceCount(thisWord), getSequenceCount(otherWord));
             if (res != 0) {
-              return res < 0 ? -1 : 1;
+              return res;
             }
           }
           // if the sequences are the same (both zeros or both ones)
@@ -1363,9 +1363,10 @@ public class ConciseSet extends AbstractIntSet implements Serializable
           otherWord--;
         }
       } else {
-        res = thisWord - otherWord; // equals getLiteralBits(thisWord) - getLiteralBits(otherWord)
+        // equals compare(getLiteralBits(thisWord), getLiteralBits(otherWord))
+        res = Integer.compare(thisWord, otherWord);
         if (res != 0) {
-          return res < 0 ? -1 : 1;
+          return res;
         }
         if (--thisIndex >= 0) {
           thisWord = this.words[thisIndex];
diff --git a/extendedset/src/main/java/org/apache/druid/extendedset/intset/ImmutableConciseSet.java b/extendedset/src/main/java/org/apache/druid/extendedset/intset/ImmutableConciseSet.java
index 06f53c8774e..43591e2b59d 100755
--- a/extendedset/src/main/java/org/apache/druid/extendedset/intset/ImmutableConciseSet.java
+++ b/extendedset/src/main/java/org/apache/druid/extendedset/intset/ImmutableConciseSet.java
@@ -216,7 +216,7 @@ public class ImmutableConciseSet
     int endIndex = length - 1;
 
     int wordsWalked = 0;
-    int last = 0;
+    int last;
 
     WordIterator iter = set.newWordIterator();
 
diff --git a/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/firehose/azure/AzureBlob.java b/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/firehose/azure/AzureBlob.java
index 32fc16ff516..eb30a16d21d 100644
--- a/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/firehose/azure/AzureBlob.java
+++ b/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/firehose/azure/AzureBlob.java
@@ -30,11 +30,11 @@ public class AzureBlob
 {
   @JsonProperty
   @NotNull
-  private String container = null;
+  private String container;
 
   @JsonProperty
   @NotNull
-  private String path = null;
+  private String path;
 
   @JsonCreator
   public AzureBlob(@JsonProperty("container") String container, @JsonProperty("path") String path)
diff --git a/extensions-contrib/cassandra-storage/src/main/java/org/apache/druid/storage/cassandra/CassandraDataSegmentPuller.java b/extensions-contrib/cassandra-storage/src/main/java/org/apache/druid/storage/cassandra/CassandraDataSegmentPuller.java
index dbb5771db8f..a94b6bfd9fd 100644
--- a/extensions-contrib/cassandra-storage/src/main/java/org/apache/druid/storage/cassandra/CassandraDataSegmentPuller.java
+++ b/extensions-contrib/cassandra-storage/src/main/java/org/apache/druid/storage/cassandra/CassandraDataSegmentPuller.java
@@ -62,9 +62,8 @@ public class CassandraDataSegmentPuller extends CassandraStorage
     final File tmpFile = new File(outDir, "index.zip");
     log.info("Pulling to temporary local cache [%s]", tmpFile.getAbsolutePath());
 
-    final FileUtils.FileCopyResult localResult;
     try {
-      localResult = RetryUtils.retry(
+      RetryUtils.retry(
           () -> {
             try (OutputStream os = new FileOutputStream(tmpFile)) {
               ChunkedStorage
diff --git a/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/firehose/cloudfiles/CloudFilesBlob.java b/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/firehose/cloudfiles/CloudFilesBlob.java
index 45fbdadd456..edc0bbb65c0 100644
--- a/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/firehose/cloudfiles/CloudFilesBlob.java
+++ b/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/firehose/cloudfiles/CloudFilesBlob.java
@@ -29,15 +29,15 @@ public class CloudFilesBlob
 {
   @JsonProperty
   @NotNull
-  private String container = null;
+  private String container;
 
   @JsonProperty
   @NotNull
-  private String path = null;
+  private String path;
 
   @JsonProperty
   @NotNull
-  private String region = null;
+  private String region;
 
   @JsonCreator
   public CloudFilesBlob(
diff --git a/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesStorageDruidModule.java b/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesStorageDruidModule.java
index 9628b411c44..c54342fd32d 100644
--- a/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesStorageDruidModule.java
+++ b/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesStorageDruidModule.java
@@ -96,7 +96,7 @@ public class CloudFilesStorageDruidModule implements DruidModule
   {
     log.info("Building Cloud Files Api...");
 
-    Iterable<com.google.inject.Module> modules = null;
+    Iterable<com.google.inject.Module> modules;
     if (config.getUseServiceNet()) {
       log.info("Configuring Cloud Files Api to use the internal service network...");
       modules = ImmutableSet.of(new SLF4JLoggingModule(), new InternalUrlModule());
diff --git a/extensions-contrib/kafka-eight-simpleConsumer/src/main/java/org/apache/druid/firehose/kafka/KafkaSimpleConsumer.java b/extensions-contrib/kafka-eight-simpleConsumer/src/main/java/org/apache/druid/firehose/kafka/KafkaSimpleConsumer.java
index ec204f9df4d..038fb2db90f 100644
--- a/extensions-contrib/kafka-eight-simpleConsumer/src/main/java/org/apache/druid/firehose/kafka/KafkaSimpleConsumer.java
+++ b/extensions-contrib/kafka-eight-simpleConsumer/src/main/java/org/apache/druid/firehose/kafka/KafkaSimpleConsumer.java
@@ -197,7 +197,7 @@ public class KafkaSimpleConsumer
         )
     );
     OffsetRequest request = new OffsetRequest(requestInfo, kafka.api.OffsetRequest.CurrentVersion(), clientId);
-    OffsetResponse response = null;
+    OffsetResponse response;
     try {
       response = consumer.getOffsetsBefore(request);
     }
@@ -219,7 +219,7 @@ public class KafkaSimpleConsumer
 
   public Iterable<BytesMessageWithOffset> fetch(long offset, int timeoutMs) throws InterruptedException
   {
-    FetchResponse response = null;
+    FetchResponse response;
     Broker previousLeader = leaderBroker;
     while (true) {
       ensureConsumer(previousLeader);
diff --git a/extensions-contrib/materialized-view-maintenance/src/main/java/org/apache/druid/indexing/materializedview/MaterializedViewSupervisor.java b/extensions-contrib/materialized-view-maintenance/src/main/java/org/apache/druid/indexing/materializedview/MaterializedViewSupervisor.java
index 41e58e9554a..2aa05e39ee4 100644
--- a/extensions-contrib/materialized-view-maintenance/src/main/java/org/apache/druid/indexing/materializedview/MaterializedViewSupervisor.java
+++ b/extensions-contrib/materialized-view-maintenance/src/main/java/org/apache/druid/indexing/materializedview/MaterializedViewSupervisor.java
@@ -327,7 +327,8 @@ public class MaterializedViewSupervisor implements Supervisor
     // use max created_date of base segments as the version of derivative segments
     Map<Interval, String> maxCreatedDate = baseSegmentsSnapshot.lhs;
     Map<Interval, String> derivativeVersion = derivativeSegmentsSnapshot.lhs;
-    SortedMap<Interval, String> sortedToBuildInterval = new TreeMap<>(Comparators.inverse(Comparators.intervalsByStartThenEnd()));
+    SortedMap<Interval, String> sortedToBuildInterval =
+        new TreeMap<>(Comparators.intervalsByStartThenEnd().reversed());
     // find the intervals to drop and to build
     MapDifference<Interval, String> difference = Maps.difference(maxCreatedDate, derivativeVersion);
     Map<Interval, String> toBuildInterval = new HashMap<>(difference.entriesOnlyOnLeft());
diff --git a/extensions-contrib/orc-extensions/src/test/java/org/apache/druid/data/input/orc/OrcIndexGeneratorJobTest.java b/extensions-contrib/orc-extensions/src/test/java/org/apache/druid/data/input/orc/OrcIndexGeneratorJobTest.java
index 9f07a235e87..6aa4715920a 100644
--- a/extensions-contrib/orc-extensions/src/test/java/org/apache/druid/data/input/orc/OrcIndexGeneratorJobTest.java
+++ b/extensions-contrib/orc-extensions/src/test/java/org/apache/druid/data/input/orc/OrcIndexGeneratorJobTest.java
@@ -54,7 +54,7 @@ import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hive.ql.exec.vector.BytesColumnVector;
 import org.apache.hadoop.hive.ql.exec.vector.LongColumnVector;
 import org.apache.hadoop.hive.ql.exec.vector.VectorizedRowBatch;
-import org.apache.hadoop.mapreduce.JobContext;
+import org.apache.hadoop.mapreduce.MRJobConfig;
 import org.apache.orc.CompressionKind;
 import org.apache.orc.OrcFile;
 import org.apache.orc.TypeDescription;
@@ -225,7 +225,7 @@ public class OrcIndexGeneratorJobTest
                 false,
                 false,
                 false,
-                ImmutableMap.of(JobContext.NUM_REDUCES, "0"), //verifies that set num reducers is ignored
+                ImmutableMap.of(MRJobConfig.NUM_REDUCES, "0"), //verifies that set num reducers is ignored
                 false,
                 true,
                 null,
diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildAggregator.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildAggregator.java
index 6d121b5a159..bd46fc5166f 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildAggregator.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildAggregator.java
@@ -19,6 +19,7 @@
 
 package org.apache.druid.query.aggregation.datasketches.quantiles;
 
+import com.yahoo.sketches.quantiles.DoublesSketch;
 import com.yahoo.sketches.quantiles.UpdateDoublesSketch;
 import org.apache.druid.query.aggregation.Aggregator;
 import org.apache.druid.segment.ColumnValueSelector;
@@ -35,7 +36,7 @@ public class DoublesSketchBuildAggregator implements Aggregator
   {
     this.valueSelector = valueSelector;
     this.size = size;
-    sketch = UpdateDoublesSketch.builder().setK(size).build();
+    sketch = DoublesSketch.builder().setK(size).build();
   }
 
   @Override
diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildBufferAggregator.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildBufferAggregator.java
index a1e52162800..ead9a6aa280 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildBufferAggregator.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildBufferAggregator.java
@@ -20,6 +20,7 @@
 package org.apache.druid.query.aggregation.datasketches.quantiles;
 
 import com.yahoo.memory.WritableMemory;
+import com.yahoo.sketches.quantiles.DoublesSketch;
 import com.yahoo.sketches.quantiles.UpdateDoublesSketch;
 import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
 import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
@@ -54,7 +55,7 @@ public class DoublesSketchBuildBufferAggregator implements BufferAggregator
   {
     final WritableMemory mem = getMemory(buffer);
     final WritableMemory region = mem.writableRegion(position, maxIntermediateSize);
-    final UpdateDoublesSketch sketch = UpdateDoublesSketch.builder().setK(size).build(region);
+    final UpdateDoublesSketch sketch = DoublesSketch.builder().setK(size).build(region);
     putSketch(buffer, position, sketch);
   }
 
diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchHolder.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchHolder.java
index 1b5b2bb3a00..1e70a7197d7 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchHolder.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchHolder.java
@@ -90,6 +90,7 @@ public class SketchHolder
 
   private static final Comparator<Memory> MEMORY_COMPARATOR = new Comparator<Memory>()
   {
+    @SuppressWarnings("SubtractionInCompareTo")
     @Override
     public int compare(Memory o1, Memory o2)
     {
diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchToQuantilesSketchPostAggregator.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchToQuantilesSketchPostAggregator.java
index 1f4575bc287..220c1cd6ac3 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchToQuantilesSketchPostAggregator.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchToQuantilesSketchPostAggregator.java
@@ -74,7 +74,7 @@ public class ArrayOfDoublesSketchToQuantilesSketchPostAggregator extends ArrayOf
   public DoublesSketch compute(final Map<String, Object> combinedAggregators)
   {
     final ArrayOfDoublesSketch sketch = (ArrayOfDoublesSketch) getField().compute(combinedAggregators);
-    final UpdateDoublesSketch qs = UpdateDoublesSketch.builder().setK(k).build();
+    final UpdateDoublesSketch qs = DoublesSketch.builder().setK(k).build();
     final ArrayOfDoublesSketchIterator it = sketch.iterator();
     while (it.next()) {
       qs.update(it.getValues()[column - 1]); // convert 1-based column number to zero-based index
diff --git a/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/quantiles/GenerateTestData.java b/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/quantiles/GenerateTestData.java
index 48d8205f56a..ea9d32851b7 100644
--- a/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/quantiles/GenerateTestData.java
+++ b/extensions-core/datasketches/src/test/java/org/apache/druid/query/aggregation/datasketches/quantiles/GenerateTestData.java
@@ -19,6 +19,7 @@
 
 package org.apache.druid.query.aggregation.datasketches.quantiles;
 
+import com.yahoo.sketches.quantiles.DoublesSketch;
 import com.yahoo.sketches.quantiles.UpdateDoublesSketch;
 import org.apache.commons.codec.binary.Base64;
 
@@ -44,7 +45,7 @@ public class GenerateTestData
     int sequenceNumber = 0;
     for (int i = 0; i < 20; i++) {
       int product = rand.nextInt(10);
-      UpdateDoublesSketch sketch = UpdateDoublesSketch.builder().build();
+      UpdateDoublesSketch sketch = DoublesSketch.builder().build();
       for (int j = 0; j < 20; j++) {
         double value = rand.nextDouble();
         buildData.write("2016010101");
diff --git a/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/DruidKerberosAuthenticationHandler.java b/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/DruidKerberosAuthenticationHandler.java
index b6f91b5369d..12ebb4be4e1 100644
--- a/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/DruidKerberosAuthenticationHandler.java
+++ b/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/DruidKerberosAuthenticationHandler.java
@@ -143,15 +143,17 @@ public class DruidKerberosAuthenticationHandler extends KerberosAuthenticationHa
   public AuthenticationToken authenticate(HttpServletRequest request, final HttpServletResponse response)
       throws IOException, AuthenticationException
   {
-    AuthenticationToken token = null;
-    String authorization = request.getHeader(org.apache.hadoop.security.authentication.client.KerberosAuthenticator.AUTHORIZATION);
+    AuthenticationToken token;
+    String authorization = request
+        .getHeader(org.apache.hadoop.security.authentication.client.KerberosAuthenticator.AUTHORIZATION);
 
-    if (authorization == null
-        || !authorization.startsWith(org.apache.hadoop.security.authentication.client.KerberosAuthenticator.NEGOTIATE)) {
+    if (authorization == null ||
+        !authorization.startsWith(org.apache.hadoop.security.authentication.client.KerberosAuthenticator.NEGOTIATE)) {
       return null;
     } else {
-      authorization = authorization.substring(org.apache.hadoop.security.authentication.client.KerberosAuthenticator.NEGOTIATE
-                                                  .length()).trim();
+      authorization = authorization
+          .substring(org.apache.hadoop.security.authentication.client.KerberosAuthenticator.NEGOTIATE.length())
+          .trim();
       final Base64 base64 = new Base64(0);
       final byte[] clientToken = base64.decode(authorization);
       final String serverName = request.getServerName();
diff --git a/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/KerberosAuthenticator.java b/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/KerberosAuthenticator.java
index 394e82625ef..07b27a69930 100644
--- a/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/KerberosAuthenticator.java
+++ b/extensions-core/druid-kerberos/src/main/java/org/apache/druid/security/kerberos/KerberosAuthenticator.java
@@ -248,7 +248,7 @@ public class KerberosAuthenticator implements Authenticator
         if (isExcluded(path)) {
           filterChain.doFilter(request, response);
         } else {
-          String clientPrincipal = null;
+          String clientPrincipal;
           try {
             Cookie[] cookies = httpReq.getCookies();
             if (cookies == null) {
diff --git a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java
index 630aa2447fd..03f45080865 100644
--- a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java
+++ b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java
@@ -73,6 +73,15 @@ import java.util.HashMap;
  */
 public class HdfsDataSegmentPusherTest
 {
+  static TestObjectMapper objectMapper;
+
+  static {
+    objectMapper = new TestObjectMapper();
+    InjectableValues.Std injectableValues = new InjectableValues.Std();
+    injectableValues.addValue(ObjectMapper.class, objectMapper);
+    injectableValues.addValue(DataSegment.PruneLoadSpecHolder.class, DataSegment.PruneLoadSpecHolder.DEFAULT);
+    objectMapper.setInjectableValues(injectableValues);
+  }
 
   @Rule
   public final TemporaryFolder tempFolder = new TemporaryFolder();
@@ -80,23 +89,15 @@ public class HdfsDataSegmentPusherTest
   @Rule
   public final ExpectedException expectedException = ExpectedException.none();
 
-  static TestObjectMapper objectMapper = new TestObjectMapper();
-
   private HdfsDataSegmentPusher hdfsDataSegmentPusher;
+
   @Before
-  public void setUp() throws IOException
+  public void setUp()
   {
     HdfsDataSegmentPusherConfig hdfsDataSegmentPusherConf = new HdfsDataSegmentPusherConfig();
     hdfsDataSegmentPusherConf.setStorageDirectory("path/to/");
     hdfsDataSegmentPusher = new HdfsDataSegmentPusher(hdfsDataSegmentPusherConf, new Configuration(true), objectMapper);
   }
-  static {
-    objectMapper = new TestObjectMapper();
-    InjectableValues.Std injectableValues = new InjectableValues.Std();
-    injectableValues.addValue(ObjectMapper.class, objectMapper);
-    injectableValues.addValue(DataSegment.PruneLoadSpecHolder.class, DataSegment.PruneLoadSpecHolder.DEFAULT);
-    objectMapper.setInjectableValues(injectableValues);
-  }
 
   @Test
   public void testPushWithScheme() throws Exception
diff --git a/extensions-core/histogram/src/main/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogram.java b/extensions-core/histogram/src/main/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogram.java
index 9c5c8e4e156..0135c8de18d 100644
--- a/extensions-core/histogram/src/main/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogram.java
+++ b/extensions-core/histogram/src/main/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogram.java
@@ -363,7 +363,6 @@ public class ApproximateHistogram
       mergeValue = true;
     }
     if (deltaLeft < minDelta) {
-      minDelta = deltaLeft;
       minPos = insertAt - 1;
       mergeValue = true;
     }
@@ -1563,7 +1562,7 @@ public class ApproximateHistogram
       int i = 0;
       int sum = 0;
       int k = 1;
-      long count = 0;
+      long count;
       while (k <= this.binCount()) {
         count = bins[k - 1];
         if (sum + count > s) {
@@ -1583,7 +1582,7 @@ public class ApproximateHistogram
         final double c = -2 * d;
         final long a = bins[i] - bins[i - 1];
         final long b = 2 * bins[i - 1];
-        double z = 0;
+        double z;
         if (a == 0) {
           z = -c / b;
         } else {
diff --git a/extensions-core/histogram/src/test/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramTest.java b/extensions-core/histogram/src/test/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramTest.java
index ddb71ed8327..c63ead315bb 100644
--- a/extensions-core/histogram/src/test/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramTest.java
+++ b/extensions-core/histogram/src/test/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramTest.java
@@ -22,6 +22,7 @@ package org.apache.druid.query.aggregation.histogram;
 import com.google.common.collect.Iterators;
 import org.apache.druid.java.util.common.StringUtils;
 import org.junit.Assert;
+import org.junit.Ignore;
 import org.junit.Test;
 
 import java.nio.ByteBuffer;
@@ -221,6 +222,7 @@ public class ApproximateHistogramTest
   }
 
     //@Test
+  @Ignore
   @SuppressWarnings("unused") //TODO rewrite using JMH and move to the benchmarks module
   public void testFoldSpeed()
   {
diff --git a/extensions-core/kafka-indexing-service/src/main/java/org/apache/druid/indexing/kafka/supervisor/KafkaSupervisor.java b/extensions-core/kafka-indexing-service/src/main/java/org/apache/druid/indexing/kafka/supervisor/KafkaSupervisor.java
index 8a199d4a3de..6609b2412c0 100644
--- a/extensions-core/kafka-indexing-service/src/main/java/org/apache/druid/indexing/kafka/supervisor/KafkaSupervisor.java
+++ b/extensions-core/kafka-indexing-service/src/main/java/org/apache/druid/indexing/kafka/supervisor/KafkaSupervisor.java
@@ -34,7 +34,6 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
-import com.google.common.collect.Lists;
 import com.google.common.primitives.Longs;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
@@ -43,6 +42,7 @@ import com.google.common.util.concurrent.MoreExecutors;
 import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.druid.indexer.TaskLocation;
 import org.apache.druid.indexer.TaskStatus;
+import org.apache.druid.indexing.common.IndexTaskClient;
 import org.apache.druid.indexing.common.TaskInfoProvider;
 import org.apache.druid.indexing.common.stats.RowIngestionMetersFactory;
 import org.apache.druid.indexing.common.task.RealtimeIndexTask;
@@ -129,7 +129,6 @@ public class KafkaSupervisor implements Supervisor
   private static final long INITIAL_GET_OFFSET_DELAY_MILLIS = 15000;
   private static final long INITIAL_EMIT_LAG_METRIC_DELAY_MILLIS = 25000;
   private static final int MAX_INITIALIZATION_RETRIES = 20;
-  private static final CopyOnWriteArrayList EMPTY_LIST = Lists.newCopyOnWriteArrayList();
 
   public static final String IS_INCREMENTAL_HANDOFF_SUPPORTED = "IS_INCREMENTAL_HANDOFF_SUPPORTED";
 
@@ -337,7 +336,7 @@ public class KafkaSupervisor implements Supervisor
     this.futureTimeoutInSeconds = Math.max(
         MINIMUM_FUTURE_TIMEOUT_IN_SECONDS,
         tuningConfig.getChatRetries() * (tuningConfig.getHttpTimeout().getStandardSeconds()
-                                         + KafkaIndexTaskClient.MAX_RETRY_WAIT_SECONDS)
+                                         + IndexTaskClient.MAX_RETRY_WAIT_SECONDS)
     );
 
     int chatThreads = (this.tuningConfig.getChatThreads() != null
@@ -468,6 +467,12 @@ public class KafkaSupervisor implements Supervisor
     }
   }
 
+  private boolean someTaskGroupsPendingCompletion(Integer groupId)
+  {
+    CopyOnWriteArrayList<TaskGroup> taskGroups = pendingCompletionTaskGroups.get(groupId);
+    return taskGroups != null && taskGroups.size() > 0;
+  }
+
   @Override
   public SupervisorReport getStatus()
   {
@@ -1341,7 +1346,7 @@ public class KafkaSupervisor implements Supervisor
                     partitionOffset.getValue() :
                     latestOffsetsFromDb.getOrDefault(partitionOffset.getKey(), partitionOffset.getValue())
                 ) == 0) && earliestConsistentSequenceId.compareAndSet(-1, sequenceCheckpoint.getKey())) || (
-                pendingCompletionTaskGroups.getOrDefault(groupId, EMPTY_LIST).size() > 0
+                someTaskGroupsPendingCompletion(groupId)
                 && earliestConsistentSequenceId.compareAndSet(-1, taskCheckpoints.firstKey()))) {
           final SortedMap<Integer, Map<Integer, Long>> latestCheckpoints = new TreeMap<>(
               taskCheckpoints.tailMap(earliestConsistentSequenceId.get())
@@ -1378,7 +1383,7 @@ public class KafkaSupervisor implements Supervisor
     }
 
     if ((tasksToKill.size() > 0 && tasksToKill.size() == taskGroup.tasks.size()) ||
-        (taskGroup.tasks.size() == 0 && pendingCompletionTaskGroups.getOrDefault(groupId, EMPTY_LIST).size() == 0)) {
+        (taskGroup.tasks.size() == 0 && !someTaskGroupsPendingCompletion(groupId))) {
       // killing all tasks or no task left in the group ?
       // clear state about the taskgroup so that get latest offset information is fetched from metadata store
       log.warn("Clearing task group [%d] information as no valid tasks left the group", groupId);
diff --git a/extensions-core/kafka-indexing-service/src/test/java/org/apache/druid/indexing/kafka/test/TestBroker.java b/extensions-core/kafka-indexing-service/src/test/java/org/apache/druid/indexing/kafka/test/TestBroker.java
index 4b8e02c2d73..a57d22b1446 100644
--- a/extensions-core/kafka-indexing-service/src/test/java/org/apache/druid/indexing/kafka/test/TestBroker.java
+++ b/extensions-core/kafka-indexing-service/src/test/java/org/apache/druid/indexing/kafka/test/TestBroker.java
@@ -29,7 +29,7 @@ import org.apache.kafka.clients.consumer.KafkaConsumer;
 import org.apache.kafka.clients.producer.KafkaProducer;
 import org.apache.kafka.common.serialization.ByteArrayDeserializer;
 import org.apache.kafka.common.serialization.ByteArraySerializer;
-import org.apache.kafka.common.utils.SystemTime;
+import org.apache.kafka.common.utils.Time;
 import scala.Some;
 import scala.collection.immutable.List$;
 
@@ -81,7 +81,7 @@ public class TestBroker implements Closeable
 
     final KafkaConfig config = new KafkaConfig(props);
 
-    server = new KafkaServer(config, SystemTime.SYSTEM, Some.apply(StringUtils.format("TestingBroker[%d]-", id)), List$.MODULE$.empty());
+    server = new KafkaServer(config, Time.SYSTEM, Some.apply(StringUtils.format("TestingBroker[%d]-", id)), List$.MODULE$.empty());
     server.startup();
   }
 
diff --git a/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/CacheSchedulerTest.java b/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/CacheSchedulerTest.java
index d22ce75f09d..41a861621dc 100644
--- a/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/CacheSchedulerTest.java
+++ b/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/CacheSchedulerTest.java
@@ -311,7 +311,7 @@ public class CacheSchedulerTest
     testDelete();
   }
 
-  public void testDelete() throws InterruptedException
+  private void testDelete() throws InterruptedException
   {
     final long period = 1_000L; // Give it some time between attempts to update
     final UriExtractionNamespace namespace = getUriExtractionNamespace(period);
diff --git a/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/JdbcExtractionNamespaceTest.java b/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/JdbcExtractionNamespaceTest.java
index 139c8a017a8..fd89b7bac68 100644
--- a/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/JdbcExtractionNamespaceTest.java
+++ b/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/cache/JdbcExtractionNamespaceTest.java
@@ -519,7 +519,7 @@ public class JdbcExtractionNamespaceTest
   private void waitForUpdates(long timeout, long numUpdates) throws InterruptedException
   {
     long startTime = System.currentTimeMillis();
-    long pre = 0L;
+    long pre;
     updateLock.lockInterruptibly();
     try {
       pre = updates.get();
@@ -527,7 +527,7 @@ public class JdbcExtractionNamespaceTest
     finally {
       updateLock.unlock();
     }
-    long post = 0L;
+    long post;
     do {
       // Sleep to spare a few cpu cycles
       Thread.sleep(5);
diff --git a/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java b/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java
index 25eedc4b174..e47adeeeaa8 100644
--- a/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java
+++ b/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java
@@ -111,7 +111,7 @@ public class ProtobufInputRowParser implements ByteBufferInputRowParser
 
     fin = this.getClass().getClassLoader().getResourceAsStream(descriptorFilePath);
     if (fin == null) {
-      URL url = null;
+      URL url;
       try {
         url = new URL(descriptorFilePath);
       }
@@ -126,7 +126,7 @@ public class ProtobufInputRowParser implements ByteBufferInputRowParser
       }
     }
 
-    DynamicSchema dynamicSchema = null;
+    DynamicSchema dynamicSchema;
     try {
       dynamicSchema = DynamicSchema.parseFrom(fin);
     }
diff --git a/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceGroupByQueryTest.java b/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceGroupByQueryTest.java
index 4f327e75793..90f61128da6 100644
--- a/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceGroupByQueryTest.java
+++ b/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceGroupByQueryTest.java
@@ -125,12 +125,12 @@ public class VarianceGroupByQueryTest
         .setDataSource(QueryRunnerTestHelper.dataSource)
         .setQuerySegmentSpec(QueryRunnerTestHelper.firstToThird)
         .setDimensions(new DefaultDimensionSpec("quality", "alias"))
-        .setAggregatorSpecs(VarianceTestHelper.rowsCount,
-                            VarianceTestHelper.indexVarianceAggr,
-                            new LongSumAggregatorFactory("idx", "index"))
-        .setPostAggregatorSpecs(
-            Collections.singletonList(VarianceTestHelper.stddevOfIndexPostAggr)
+        .setAggregatorSpecs(
+            QueryRunnerTestHelper.rowsCount,
+            VarianceTestHelper.indexVarianceAggr,
+            new LongSumAggregatorFactory("idx", "index")
         )
+        .setPostAggregatorSpecs(Collections.singletonList(VarianceTestHelper.stddevOfIndexPostAggr))
         .setGranularity(QueryRunnerTestHelper.dayGran)
         .build();
 
@@ -178,12 +178,14 @@ public class VarianceGroupByQueryTest
 
     GroupByQuery query = GroupByQuery
         .builder()
-        .setDataSource(VarianceTestHelper.dataSource)
+        .setDataSource(QueryRunnerTestHelper.dataSource)
         .setInterval("2011-04-02/2011-04-04")
         .setDimensions(new DefaultDimensionSpec("quality", "alias"))
-        .setAggregatorSpecs(VarianceTestHelper.rowsCount,
-                            VarianceTestHelper.indexLongSum,
-                            VarianceTestHelper.indexVarianceAggr)
+        .setAggregatorSpecs(
+            QueryRunnerTestHelper.rowsCount,
+            QueryRunnerTestHelper.indexLongSum,
+            VarianceTestHelper.indexVarianceAggr
+        )
         .setPostAggregatorSpecs(ImmutableList.of(VarianceTestHelper.stddevOfIndexPostAggr))
         .setGranularity(new PeriodGranularity(new Period("P1M"), null, null))
         .setHavingSpec(
diff --git a/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceTimeseriesQueryTest.java b/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceTimeseriesQueryTest.java
index c1a98d0984c..c5dcecea9bf 100644
--- a/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceTimeseriesQueryTest.java
+++ b/extensions-core/stats/src/test/java/org/apache/druid/query/aggregation/variance/VarianceTimeseriesQueryTest.java
@@ -23,6 +23,7 @@ import org.apache.druid.java.util.common.DateTimes;
 import org.apache.druid.query.Druids;
 import org.apache.druid.query.QueryPlus;
 import org.apache.druid.query.QueryRunner;
+import org.apache.druid.query.QueryRunnerTestHelper;
 import org.apache.druid.query.Result;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.timeseries.TimeseriesQuery;
@@ -59,13 +60,13 @@ public class VarianceTimeseriesQueryTest
   public void testTimeseriesWithNullFilterOnNonExistentDimension()
   {
     TimeseriesQuery query = Druids.newTimeseriesQueryBuilder()
-                                  .dataSource(VarianceTestHelper.dataSource)
-                                  .granularity(VarianceTestHelper.dayGran)
+                                  .dataSource(QueryRunnerTestHelper.dataSource)
+                                  .granularity(QueryRunnerTestHelper.dayGran)
                                   .filters("bobby", null)
-                                  .intervals(VarianceTestHelper.firstToThird)
+                                  .intervals(QueryRunnerTestHelper.firstToThird)
                                   .aggregators(VarianceTestHelper.commonPlusVarAggregators)
                                   .postAggregators(
-                                      VarianceTestHelper.addRowsIndexConstant,
+                                      QueryRunnerTestHelper.addRowsIndexConstant,
                                       VarianceTestHelper.stddevOfIndexPostAggr
                                   )
                                   .descending(descending)
@@ -75,11 +76,11 @@ public class VarianceTimeseriesQueryTest
         new Result<>(
             DateTimes.of("2011-04-01"),
             new TimeseriesResultValue(
-                VarianceTestHelper.of(
+                QueryRunnerTestHelper.of(
                     "rows", 13L,
                     "index", 6626.151596069336,
                     "addRowsIndexConstant", 6640.151596069336,
-                    "uniques", VarianceTestHelper.UNIQUES_9,
+                    "uniques", QueryRunnerTestHelper.UNIQUES_9,
                     "index_var", descending ? 368885.6897238851 : 368885.689155086,
                     "index_stddev", descending ? 607.3596049490657 : 607.35960448081
                 )
@@ -88,11 +89,11 @@ public class VarianceTimeseriesQueryTest
         new Result<>(
             DateTimes.of("2011-04-02"),
             new TimeseriesResultValue(
-                VarianceTestHelper.of(
+                QueryRunnerTestHelper.of(
                     "rows", 13L,
                     "index", 5833.2095947265625,
                     "addRowsIndexConstant", 5847.2095947265625,
-                    "uniques", VarianceTestHelper.UNIQUES_9,
+                    "uniques", QueryRunnerTestHelper.UNIQUES_9,
                     "index_var", descending ? 259061.6037088883 : 259061.60216419376,
                     "index_stddev", descending ? 508.9809463122252 : 508.98094479478675
                 )
diff --git a/hll/src/main/java/org/apache/druid/hll/HyperLogLogCollector.java b/hll/src/main/java/org/apache/druid/hll/HyperLogLogCollector.java
index bc8dbbbebe6..5fd7df778de 100644
--- a/hll/src/main/java/org/apache/druid/hll/HyperLogLogCollector.java
+++ b/hll/src/main/java/org/apache/druid/hll/HyperLogLogCollector.java
@@ -358,7 +358,7 @@ public abstract class HyperLogLogCollector implements Comparable<HyperLogLogColl
     short numNonZeroRegisters = addNibbleRegister(bucket, (byte) ((0xff & positionOf1) - registerOffset));
     setNumNonZeroRegisters(numNonZeroRegisters);
     if (numNonZeroRegisters == NUM_BUCKETS) {
-      setRegisterOffset(++registerOffset);
+      setRegisterOffset((byte) (registerOffset + 1));
       setNumNonZeroRegisters(decrementBuckets());
     }
   }
@@ -421,7 +421,7 @@ public abstract class HyperLogLogCollector implements Comparable<HyperLogLogColl
         }
         if (numNonZero == NUM_BUCKETS) {
           numNonZero = decrementBuckets();
-          setRegisterOffset(++myOffset);
+          setRegisterOffset((byte) (myOffset + 1));
           setNumNonZeroRegisters(numNonZero);
         }
       } else { // dense
@@ -437,7 +437,7 @@ public abstract class HyperLogLogCollector implements Comparable<HyperLogLogColl
         }
         if (numNonZero == NUM_BUCKETS) {
           numNonZero = decrementBuckets();
-          setRegisterOffset(++myOffset);
+          setRegisterOffset((byte) (myOffset + 1));
           setNumNonZeroRegisters(numNonZero);
         }
       }
diff --git a/hll/src/test/java/org/apache/druid/hll/HyperLogLogCollectorBenchmark.java b/hll/src/test/java/org/apache/druid/hll/HyperLogLogCollectorBenchmark.java
index aea0e4265e3..938bd9c7345 100644
--- a/hll/src/test/java/org/apache/druid/hll/HyperLogLogCollectorBenchmark.java
+++ b/hll/src/test/java/org/apache/druid/hll/HyperLogLogCollectorBenchmark.java
@@ -41,6 +41,7 @@ public class HyperLogLogCollectorBenchmark extends SimpleBenchmark
 {
   private final HashFunction fn = Hashing.murmur3_128();
 
+  @SuppressWarnings("MismatchedQueryAndUpdateOfCollection") // TODO understand if this field should be used or not
   private final List<HyperLogLogCollector> collectors = new ArrayList<>();
 
   @Param({"true"}) boolean targetIsDirect;
diff --git a/indexing-hadoop/src/test/java/org/apache/druid/indexer/IndexGeneratorJobTest.java b/indexing-hadoop/src/test/java/org/apache/druid/indexer/IndexGeneratorJobTest.java
index d19bcf55fcd..8e191c7fba9 100644
--- a/indexing-hadoop/src/test/java/org/apache/druid/indexer/IndexGeneratorJobTest.java
+++ b/indexing-hadoop/src/test/java/org/apache/druid/indexer/IndexGeneratorJobTest.java
@@ -54,7 +54,7 @@ import org.apache.hadoop.io.BytesWritable;
 import org.apache.hadoop.io.SequenceFile;
 import org.apache.hadoop.io.SequenceFile.Writer;
 import org.apache.hadoop.io.compress.CompressionCodec;
-import org.apache.hadoop.mapreduce.JobContext;
+import org.apache.hadoop.mapreduce.MRJobConfig;
 import org.apache.hadoop.mapreduce.lib.input.SequenceFileInputFormat;
 import org.joda.time.DateTime;
 import org.joda.time.DateTimeComparator;
@@ -524,7 +524,7 @@ public class IndexGeneratorJobTest
                 false,
                 false,
                 false,
-                ImmutableMap.of(JobContext.NUM_REDUCES, "0"), //verifies that set num reducers is ignored
+                ImmutableMap.of(MRJobConfig.NUM_REDUCES, "0"), //verifies that set num reducers is ignored
                 false,
                 useCombiner,
                 null,
diff --git a/indexing-service/src/main/java/org/apache/druid/indexing/common/task/HadoopIndexTask.java b/indexing-service/src/main/java/org/apache/druid/indexing/common/task/HadoopIndexTask.java
index 40cd7d519e9..104123fc100 100644
--- a/indexing-service/src/main/java/org/apache/druid/indexing/common/task/HadoopIndexTask.java
+++ b/indexing-service/src/main/java/org/apache/druid/indexing/common/task/HadoopIndexTask.java
@@ -280,7 +280,7 @@ public class HadoopIndexTask extends HadoopTask implements ChatHandler
         toolbox.getSegmentPusher().getPathForHadoop()
     };
 
-    HadoopIngestionSpec indexerSchema = null;
+    HadoopIngestionSpec indexerSchema;
     final ClassLoader oldLoader = Thread.currentThread().getContextClassLoader();
     Class<?> determinePartitionsRunnerClass = determinePartitionsInnerProcessingRunner.getClass();
     Method determinePartitionsInnerProcessingRunTask = determinePartitionsRunnerClass.getMethod(
diff --git a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/hrtr/HttpRemoteTaskRunner.java b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/hrtr/HttpRemoteTaskRunner.java
index 899be15789a..3d36000c9af 100644
--- a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/hrtr/HttpRemoteTaskRunner.java
+++ b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/hrtr/HttpRemoteTaskRunner.java
@@ -963,7 +963,7 @@ public class HttpRemoteTaskRunner implements WorkerTaskRunner, TaskLogStreamer
     pendingTasksExec.execute(
         () -> {
           while (!Thread.interrupted() && lifecycleLock.awaitStarted(1, TimeUnit.MILLISECONDS)) {
-            ImmutableWorkerInfo immutableWorker = null;
+            ImmutableWorkerInfo immutableWorker;
             HttpRemoteTaskRunnerWorkItem taskItem = null;
             try {
               synchronized (statusLock) {
diff --git a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/supervisor/SupervisorManager.java b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/supervisor/SupervisorManager.java
index f2c78a66b8a..4a8ae2f96cd 100644
--- a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/supervisor/SupervisorManager.java
+++ b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/supervisor/SupervisorManager.java
@@ -289,7 +289,7 @@ public class SupervisorManager
       metadataSupervisorManager.insert(id, spec);
     }
 
-    Supervisor supervisor = null;
+    Supervisor supervisor;
     try {
       supervisor = spec.createSupervisor();
       supervisor.start();
diff --git a/indexing-service/src/main/java/org/apache/druid/indexing/worker/WorkerTaskManager.java b/indexing-service/src/main/java/org/apache/druid/indexing/worker/WorkerTaskManager.java
index a858f88fd7e..561a6e1befa 100644
--- a/indexing-service/src/main/java/org/apache/druid/indexing/worker/WorkerTaskManager.java
+++ b/indexing-service/src/main/java/org/apache/druid/indexing/worker/WorkerTaskManager.java
@@ -576,7 +576,7 @@ public abstract class WorkerTaskManager
     @Override
     public void handle()
     {
-      TaskAnnouncement announcement = null;
+      TaskAnnouncement announcement;
       synchronized (lock) {
         if (runningTasks.containsKey(task.getId()) || completedTasks.containsKey(task.getId())) {
           log.warn(
diff --git a/indexing-service/src/test/java/org/apache/druid/indexing/firehose/IngestSegmentFirehoseFactoryTest.java b/indexing-service/src/test/java/org/apache/druid/indexing/firehose/IngestSegmentFirehoseFactoryTest.java
index 7fc311a3f6d..9db06583a80 100644
--- a/indexing-service/src/test/java/org/apache/druid/indexing/firehose/IngestSegmentFirehoseFactoryTest.java
+++ b/indexing-service/src/test/java/org/apache/druid/indexing/firehose/IngestSegmentFirehoseFactoryTest.java
@@ -174,7 +174,6 @@ public class IngestSegmentFirehoseFactoryTest
     final IndexerSQLMetadataStorageCoordinator mdc = new IndexerSQLMetadataStorageCoordinator(null, null, null)
     {
       private final Set<DataSegment> published = new HashSet<>();
-      private final Set<DataSegment> nuked = new HashSet<>();
 
       @Override
       public List<DataSegment> getUsedSegmentsForInterval(String dataSource, Interval interval)
@@ -210,7 +209,7 @@ public class IngestSegmentFirehoseFactoryTest
       @Override
       public void deleteSegments(Set<DataSegment> segments)
       {
-        nuked.addAll(segments);
+        // do nothing
       }
     };
     final LocalTaskActionClientFactory tac = new LocalTaskActionClientFactory(
@@ -596,7 +595,6 @@ public class IngestSegmentFirehoseFactoryTest
     final int numSegmentsPerPartitionChunk = 5;
     final int numPartitionChunksPerTimelineObject = 10;
     final int numSegments = numSegmentsPerPartitionChunk * numPartitionChunksPerTimelineObject;
-    final List<DataSegment> segments = new ArrayList<>(numSegments);
     final Interval interval = Intervals.of("2017-01-01/2017-01-02");
     final String version = "1";
 
@@ -621,7 +619,6 @@ public class IngestSegmentFirehoseFactoryTest
             1,
             1
         );
-        segments.add(segment);
 
         final PartitionChunk<DataSegment> partitionChunk = new NumberedPartitionChunk<>(
             i,
diff --git a/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentKiller.java b/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentKiller.java
index 515db19dff7..33421eb1a5c 100644
--- a/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentKiller.java
+++ b/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentKiller.java
@@ -19,20 +19,15 @@
 
 package org.apache.druid.indexing.test;
 
-import com.google.common.collect.Sets;
 import org.apache.druid.segment.loading.DataSegmentKiller;
 import org.apache.druid.timeline.DataSegment;
 
-import java.util.Set;
-
 public class TestDataSegmentKiller implements DataSegmentKiller
 {
-  private final Set<DataSegment> killedSegments = Sets.newConcurrentHashSet();
-
   @Override
   public void kill(DataSegment segment)
   {
-    killedSegments.add(segment);
+    // do nothing
   }
 
   @Override
diff --git a/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentPusher.java b/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentPusher.java
index 8a47742cdb9..543fa76d6d7 100644
--- a/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentPusher.java
+++ b/indexing-service/src/test/java/org/apache/druid/indexing/test/TestDataSegmentPusher.java
@@ -19,19 +19,15 @@
 
 package org.apache.druid.indexing.test;
 
-import com.google.common.collect.Sets;
 import org.apache.druid.segment.loading.DataSegmentPusher;
 import org.apache.druid.timeline.DataSegment;
 
 import java.io.File;
 import java.net.URI;
 import java.util.Map;
-import java.util.Set;
 
 public class TestDataSegmentPusher implements DataSegmentPusher
 {
-  private final Set<DataSegment> pushedSegments = Sets.newConcurrentHashSet();
-
   @Deprecated
   @Override
   public String getPathForHadoop(String dataSource)
@@ -48,7 +44,6 @@ public class TestDataSegmentPusher implements DataSegmentPusher
   @Override
   public DataSegment push(File file, DataSegment segment, boolean useUniquePath)
   {
-    pushedSegments.add(segment);
     return segment;
   }
 
diff --git a/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java b/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java
index eff8989b23a..a3a6683395b 100644
--- a/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java
+++ b/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java
@@ -88,12 +88,12 @@ public class CoordinatorResourceTestClient
   // return a list of the segment dates for the specified datasource
   public List<String> getMetadataSegments(final String dataSource)
   {
-    ArrayList<String> segments = null;
+    ArrayList<String> segments;
     try {
       StatusResponseHolder response = makeRequest(HttpMethod.GET, getMetadataSegmentsURL(dataSource));
 
       segments = jsonMapper.readValue(
-          response.getContent(), new TypeReference<ArrayList<String>>()
+          response.getContent(), new TypeReference<List<String>>()
           {
           }
       );
@@ -107,12 +107,12 @@ public class CoordinatorResourceTestClient
   // return a list of the segment dates for the specified datasource
   public List<String> getSegmentIntervals(final String dataSource)
   {
-    ArrayList<String> segments = null;
+    ArrayList<String> segments;
     try {
       StatusResponseHolder response = makeRequest(HttpMethod.GET, getIntervalsURL(dataSource));
 
       segments = jsonMapper.readValue(
-          response.getContent(), new TypeReference<ArrayList<String>>()
+          response.getContent(), new TypeReference<List<String>>()
           {
           }
       );
@@ -125,7 +125,7 @@ public class CoordinatorResourceTestClient
 
   private Map<String, Integer> getLoadStatus()
   {
-    Map<String, Integer> status = null;
+    Map<String, Integer> status;
     try {
       StatusResponseHolder response = makeRequest(HttpMethod.GET, getLoadStatusURL());
 
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java b/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java
index ebfe22d9595..6e6b298aedf 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java
@@ -60,7 +60,7 @@ public class ITHadoopIndexTest extends AbstractIndexerTest
 
   private void loadData(String hadoopDir)
   {
-    String indexerSpec = "";
+    String indexerSpec;
 
     try {
       LOG.info("indexerFile name: [%s]", BATCH_TASK);
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java
index 4eaa40c26bd..3d7802a7a47 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java
@@ -100,7 +100,7 @@ public abstract class AbstractITRealtimeIndexTaskTest extends AbstractIndexerTes
       TimeUnit.SECONDS.sleep(5);
 
       // put the timestamps into the query structure
-      String query_response_template = null;
+      String query_response_template;
       InputStream is = ITRealtimeIndexTaskTest.class.getResourceAsStream(getQueriesResource());
       if (null == is) {
         throw new ISE("could not open query file: %s", getQueriesResource());
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java
index e6ca33d1d61..bdd0df78ee3 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java
@@ -61,7 +61,7 @@ public class ITAppenderatorDriverRealtimeIndexTaskTest extends AbstractITRealtim
     final ServerDiscoverySelector eventReceiverSelector = factory.createSelector(EVENT_RECEIVER_SERVICE_NAME);
     eventReceiverSelector.start();
     BufferedReader reader = null;
-    InputStreamReader isr = null;
+    InputStreamReader isr;
     try {
       isr = new InputStreamReader(
           ITRealtimeIndexTaskTest.class.getResourceAsStream(EVENT_DATA_FILE),
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java
index 6e29c3ae097..4078984e854 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java
@@ -197,7 +197,6 @@ public class ITKafkaTest extends AbstractIndexerTest
       consumerProperties.put("zookeeper.connection.timeout.ms", "15000");
       consumerProperties.put("zookeeper.sync.time.ms", "5000");
       consumerProperties.put("group.id", Long.toString(System.currentTimeMillis()));
-      consumerProperties.put("zookeeper.sync.time.ms", "5000");
       consumerProperties.put("fetch.message.max.bytes", "1048586");
       consumerProperties.put("auto.offset.reset", "smallest");
       consumerProperties.put("auto.commit.enable", "false");
@@ -249,20 +248,20 @@ public class ITKafkaTest extends AbstractIndexerTest
     segmentsExist = true;
 
     // put the timestamps into the query structure
-    String query_response_template = null;
+    String queryResponseTemplate;
     InputStream is = ITKafkaTest.class.getResourceAsStream(QUERIES_FILE);
     if (null == is) {
       throw new ISE("could not open query file: %s", QUERIES_FILE);
     }
 
     try {
-      query_response_template = IOUtils.toString(is, "UTF-8");
+      queryResponseTemplate = IOUtils.toString(is, "UTF-8");
     }
     catch (IOException e) {
       throw new ISE(e, "could not read query file: %s", QUERIES_FILE);
     }
 
-    String queryStr = query_response_template
+    String queryStr = queryResponseTemplate
         .replaceAll("%%DATASOURCE%%", DATASOURCE)
         // time boundary
         .replace("%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java
index 75c43fc3940..af30db33474 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java
@@ -74,7 +74,7 @@ public class ITRealtimeIndexTaskTest extends AbstractITRealtimeIndexTaskTest
     final ServerDiscoverySelector eventReceiverSelector = factory.createSelector(EVENT_RECEIVER_SERVICE_NAME);
     eventReceiverSelector.start();
     BufferedReader reader = null;
-    InputStreamReader isr = null;
+    InputStreamReader isr;
     try {
       isr = new InputStreamReader(
           ITRealtimeIndexTaskTest.class.getResourceAsStream(EVENT_DATA_FILE),
diff --git a/pom.xml b/pom.xml
index 554eb064ad4..d5814ada7b3 100644
--- a/pom.xml
+++ b/pom.xml
@@ -337,7 +337,7 @@
             <dependency>
                 <groupId>com.google.errorprone</groupId>
                 <artifactId>error_prone_annotations</artifactId>
-                <version>2.2.0</version>
+                <version>2.3.2</version>
             </dependency>
             <dependency>
                 <groupId>com.ibm.icu</groupId>
@@ -1265,8 +1265,8 @@
                                 <arg>-Xep:PreconditionsInvalidPlaceholder:ERROR</arg>
                                 <arg>-Xep:MissingOverride:ERROR</arg>
                                 <arg>-Xep:DefaultCharset:ERROR</arg>
+                                <arg>-Xep:QualifierOrScopeOnInjectMethod:ERROR</arg>
 
-                                <arg>-Xep:ArgumentParameterSwap</arg>
                                 <arg>-Xep:AssistedInjectAndInjectOnSameConstructor</arg>
                                 <arg>-Xep:AutoFactoryAtInject</arg>
                                 <arg>-Xep:ClassName</arg>
@@ -1289,7 +1289,6 @@
                                 <arg>-Xep:NumericEquality</arg>
                                 <arg>-Xep:ParameterPackage</arg>
                                 <arg>-Xep:ProtoStringFieldReferenceEquality</arg>
-                                <arg>-Xep:QualifierOnMethodWithoutProvides</arg>
                                 <arg>-Xep:UnlockMethod</arg>
                             </compilerArgs>
                         </configuration>
@@ -1297,14 +1296,14 @@
                             <dependency>
                                 <groupId>org.codehaus.plexus</groupId>
                                 <artifactId>plexus-compiler-javac-errorprone</artifactId>
-                                <version>2.8.1</version>
+                                <version>2.8.5</version>
                             </dependency>
                             <!-- override plexus-compiler-javac-errorprone's dependency on
                                  Error Prone with the latest version -->
                             <dependency>
                                 <groupId>com.google.errorprone</groupId>
                                 <artifactId>error_prone_core</artifactId>
-                                <version>2.0.19</version>
+                                <version>2.3.2</version>
                             </dependency>
                         </dependencies>
                     </plugin>
diff --git a/processing/src/main/java/org/apache/druid/query/groupby/GroupByQuery.java b/processing/src/main/java/org/apache/druid/query/groupby/GroupByQuery.java
index 9975c817025..1c7fb6c1408 100644
--- a/processing/src/main/java/org/apache/druid/query/groupby/GroupByQuery.java
+++ b/processing/src/main/java/org/apache/druid/query/groupby/GroupByQuery.java
@@ -95,11 +95,14 @@ public class GroupByQuery extends BaseQuery<Row>
 
   private final VirtualColumns virtualColumns;
   private final LimitSpec limitSpec;
+  @Nullable
   private final HavingSpec havingSpec;
+  @Nullable
   private final DimFilter dimFilter;
   private final List<DimensionSpec> dimensions;
   private final List<AggregatorFactory> aggregatorSpecs;
   private final List<PostAggregator> postAggregatorSpecs;
+  @Nullable
   private final List<List<String>> subtotalsSpec;
 
   private final boolean applyLimitPushDown;
@@ -115,9 +118,9 @@ public class GroupByQuery extends BaseQuery<Row>
       @JsonProperty("dimensions") List<DimensionSpec> dimensions,
       @JsonProperty("aggregations") List<AggregatorFactory> aggregatorSpecs,
       @JsonProperty("postAggregations") List<PostAggregator> postAggregatorSpecs,
-      @JsonProperty("having") HavingSpec havingSpec,
+      @JsonProperty("having") @Nullable HavingSpec havingSpec,
       @JsonProperty("limitSpec") LimitSpec limitSpec,
-      @JsonProperty("subtotalsSpec") List<List<String>> subtotalsSpec,
+      @JsonProperty("subtotalsSpec") @Nullable List<List<String>> subtotalsSpec,
       @JsonProperty("context") Map<String, Object> context
   )
   {
@@ -168,12 +171,12 @@ public class GroupByQuery extends BaseQuery<Row>
       final DataSource dataSource,
       final QuerySegmentSpec querySegmentSpec,
       final VirtualColumns virtualColumns,
-      final DimFilter dimFilter,
+      final @Nullable DimFilter dimFilter,
       final Granularity granularity,
-      final List<DimensionSpec> dimensions,
-      final List<AggregatorFactory> aggregatorSpecs,
-      final List<PostAggregator> postAggregatorSpecs,
-      final HavingSpec havingSpec,
+      final @Nullable List<DimensionSpec> dimensions,
+      final @Nullable List<AggregatorFactory> aggregatorSpecs,
+      final @Nullable List<PostAggregator> postAggregatorSpecs,
+      final @Nullable HavingSpec havingSpec,
       final LimitSpec limitSpec,
       final @Nullable List<List<String>> subtotalsSpec,
       final @Nullable Function<Sequence<Row>, Sequence<Row>> postProcessingFn,
@@ -198,7 +201,7 @@ public class GroupByQuery extends BaseQuery<Row>
     this.havingSpec = havingSpec;
     this.limitSpec = LimitSpec.nullToNoopLimitSpec(limitSpec);
 
-    this.subtotalsSpec = verifySubtotalsSpec(subtotalsSpec, dimensions);
+    this.subtotalsSpec = verifySubtotalsSpec(subtotalsSpec, this.dimensions);
 
     // Verify no duplicate names between dimensions, aggregators, and postAggregators.
     // They will all end up in the same namespace in the returned Rows and we can't have them clobbering each other.
@@ -211,7 +214,11 @@ public class GroupByQuery extends BaseQuery<Row>
     this.applyLimitPushDown = determineApplyLimitPushDown();
   }
 
-  private List<List<String>> verifySubtotalsSpec(List<List<String>> subtotalsSpec, List<DimensionSpec> dimensions)
+  @Nullable
+  private List<List<String>> verifySubtotalsSpec(
+      @Nullable List<List<String>> subtotalsSpec,
+      List<DimensionSpec> dimensions
+  )
   {
     // if subtotalsSpec exists then validate that all are subsets of dimensions spec and are in same order.
     // For example if we had {D1, D2, D3} in dimensions spec then
@@ -736,20 +743,37 @@ public class GroupByQuery extends BaseQuery<Row>
 
   public static class Builder
   {
+    @Nullable
+    private static List<List<String>> copySubtotalSpec(@Nullable List<List<String>> subtotalsSpec)
+    {
+      if (subtotalsSpec == null) {
+        return null;
+      }
+      return subtotalsSpec.stream().map(ArrayList::new).collect(Collectors.toList());
+    }
+
     private DataSource dataSource;
     private QuerySegmentSpec querySegmentSpec;
     private VirtualColumns virtualColumns;
+    @Nullable
     private DimFilter dimFilter;
     private Granularity granularity;
+    @Nullable
     private List<DimensionSpec> dimensions;
+    @Nullable
     private List<AggregatorFactory> aggregatorSpecs;
+    @Nullable
     private List<PostAggregator> postAggregatorSpecs;
+    @Nullable
     private HavingSpec havingSpec;
 
     private Map<String, Object> context;
 
+    @Nullable
     private List<List<String>> subtotalsSpec = null;
+    @Nullable
     private LimitSpec limitSpec = null;
+    @Nullable
     private Function<Sequence<Row>, Sequence<Row>> postProcessingFn;
     private List<OrderByColumnSpec> orderByColumnSpecs = new ArrayList<>();
     private int limit = Integer.MAX_VALUE;
@@ -787,6 +811,7 @@ public class GroupByQuery extends BaseQuery<Row>
       postAggregatorSpecs = builder.postAggregatorSpecs;
       havingSpec = builder.havingSpec;
       limitSpec = builder.limitSpec;
+      subtotalsSpec = copySubtotalSpec(builder.subtotalsSpec);
       postProcessingFn = builder.postProcessingFn;
       limit = builder.limit;
       orderByColumnSpecs = new ArrayList<>(builder.orderByColumnSpecs);
diff --git a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferArrayGrouper.java b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferArrayGrouper.java
index 67f4232df96..4bc541f4a3c 100644
--- a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferArrayGrouper.java
+++ b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferArrayGrouper.java
@@ -233,7 +233,7 @@ public class BufferArrayGrouper implements IntGrouper
 
     return new CloseableIterator<Entry<Integer>>()
     {
-      int cur = -1;
+      int cur;
       boolean findNext = false;
 
       {
diff --git a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferHashGrouper.java b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferHashGrouper.java
index ca3b6c83412..5f54fad9133 100644
--- a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferHashGrouper.java
+++ b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferHashGrouper.java
@@ -173,6 +173,7 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
     }
 
     if (sorted) {
+      @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
       final List<Integer> wrappedOffsets = new AbstractList<Integer>()
       {
         @Override
diff --git a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/LimitedBufferHashGrouper.java b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/LimitedBufferHashGrouper.java
index 2ec78598891..c8d97eafc1b 100644
--- a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/LimitedBufferHashGrouper.java
+++ b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/LimitedBufferHashGrouper.java
@@ -254,6 +254,7 @@ public class LimitedBufferHashGrouper<KeyType> extends AbstractBufferHashGrouper
   {
     final int size = offsetHeap.getHeapSize();
 
+    @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
     final List<Integer> wrappedOffsets = new AbstractList<Integer>()
     {
       @Override
diff --git a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/SpillingGrouper.java b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/SpillingGrouper.java
index a24798342e0..5dce77ffcb8 100644
--- a/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/SpillingGrouper.java
+++ b/processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/SpillingGrouper.java
@@ -72,7 +72,7 @@ public class SpillingGrouper<KeyType> implements Grouper<KeyType>
   private final List<File> dictionaryFiles = new ArrayList<>();
   private final boolean sortHasNonGroupingFields;
 
-  private boolean spillingAllowed = false;
+  private boolean spillingAllowed;
 
   public SpillingGrouper(
       final Supplier<ByteBuffer> bufferSupplier,
diff --git a/processing/src/main/java/org/apache/druid/query/ordering/StringComparators.java b/processing/src/main/java/org/apache/druid/query/ordering/StringComparators.java
index 1f991737ee2..dae5cdac2bd 100644
--- a/processing/src/main/java/org/apache/druid/query/ordering/StringComparators.java
+++ b/processing/src/main/java/org/apache/druid/query/ordering/StringComparators.java
@@ -122,7 +122,7 @@ public class StringComparators
         int ch1 = str1.codePointAt(pos[0]);
         int ch2 = str2.codePointAt(pos[1]);
 
-        int result = 0;
+        int result;
 
         if (isDigit(ch1)) {
           result = isDigit(ch2) ? compareNumbers(str1, str2, pos) : -1;
@@ -135,7 +135,7 @@ public class StringComparators
         }
       }
 
-      return str1.length() - str2.length();
+      return Integer.compare(str1.length(), str2.length());
     }
 
     private int compareNumbers(String str0, String str1, int[] pos)
diff --git a/processing/src/main/java/org/apache/druid/query/scan/ScanQueryLimitRowIterator.java b/processing/src/main/java/org/apache/druid/query/scan/ScanQueryLimitRowIterator.java
index f07647aee58..b655b21a155 100644
--- a/processing/src/main/java/org/apache/druid/query/scan/ScanQueryLimitRowIterator.java
+++ b/processing/src/main/java/org/apache/druid/query/scan/ScanQueryLimitRowIterator.java
@@ -33,7 +33,7 @@ public class ScanQueryLimitRowIterator implements CloseableIterator<ScanResultVa
 {
   private Yielder<ScanResultValue> yielder;
   private String resultFormat;
-  private long limit = 0;
+  private long limit;
   private long count = 0;
 
   public ScanQueryLimitRowIterator(
diff --git a/processing/src/main/java/org/apache/druid/query/search/SearchQueryQueryToolChest.java b/processing/src/main/java/org/apache/druid/query/search/SearchQueryQueryToolChest.java
index 8f11e4b5919..88291845565 100644
--- a/processing/src/main/java/org/apache/druid/query/search/SearchQueryQueryToolChest.java
+++ b/processing/src/main/java/org/apache/druid/query/search/SearchQueryQueryToolChest.java
@@ -285,22 +285,22 @@ public class SearchQueryQueryToolChest extends QueryToolChest<Result<SearchResul
                               @Override
                               public SearchHit apply(@Nullable Object input)
                               {
-                                String dim = null;
-                                String val = null;
-                                Integer cnt = null;
+                                String dim;
+                                String val;
+                                Integer count;
                                 if (input instanceof Map) {
                                   dim = outputNameMap.get((String) ((Map) input).get("dimension"));
                                   val = (String) ((Map) input).get("value");
-                                  cnt = (Integer) ((Map) input).get("count");
+                                  count = (Integer) ((Map) input).get("count");
                                 } else if (input instanceof SearchHit) {
                                   SearchHit cached = (SearchHit) input;
                                   dim = outputNameMap.get(cached.getDimension());
                                   val = cached.getValue();
-                                  cnt = cached.getCount();
+                                  count = cached.getCount();
                                 } else {
                                   throw new IAE("Unknown format [%s]", input.getClass());
                                 }
-                                return new SearchHit(dim, val, cnt);
+                                return new SearchHit(dim, val, count);
                               }
                             }
                         )
diff --git a/processing/src/main/java/org/apache/druid/query/select/SelectResultValueBuilder.java b/processing/src/main/java/org/apache/druid/query/select/SelectResultValueBuilder.java
index 8f98cfd3cc4..5f2cac5b8f9 100644
--- a/processing/src/main/java/org/apache/druid/query/select/SelectResultValueBuilder.java
+++ b/processing/src/main/java/org/apache/druid/query/select/SelectResultValueBuilder.java
@@ -23,7 +23,6 @@ import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.MinMaxPriorityQueue;
 import com.google.common.primitives.Longs;
-import org.apache.druid.java.util.common.guava.Comparators;
 import org.apache.druid.query.Result;
 import org.joda.time.DateTime;
 
@@ -137,7 +136,7 @@ public class SelectResultValueBuilder
     protected Queue<EventHolder> instantiatePQueue()
     {
       int threshold = pagingSpec.getThreshold();
-      return MinMaxPriorityQueue.orderedBy(descending ? Comparators.inverse(comparator) : comparator)
+      return MinMaxPriorityQueue.orderedBy(descending ? comparator.reversed() : comparator)
                                 .maximumSize(threshold > 0 ? threshold : Integer.MAX_VALUE)
                                 .create();
     }
diff --git a/processing/src/main/java/org/apache/druid/query/topn/AggregateTopNMetricFirstAlgorithm.java b/processing/src/main/java/org/apache/druid/query/topn/AggregateTopNMetricFirstAlgorithm.java
index 20735111935..270ec164086 100644
--- a/processing/src/main/java/org/apache/druid/query/topn/AggregateTopNMetricFirstAlgorithm.java
+++ b/processing/src/main/java/org/apache/druid/query/topn/AggregateTopNMetricFirstAlgorithm.java
@@ -84,7 +84,7 @@ public class AggregateTopNMetricFirstAlgorithm implements TopNAlgorithm<int[], T
 
     PooledTopNAlgorithm singleMetricAlgo = new PooledTopNAlgorithm(storageAdapter, singleMetricQuery, bufferPool);
     PooledTopNAlgorithm.PooledTopNParams singleMetricParam = null;
-    int[] dimValSelector = null;
+    int[] dimValSelector;
     try {
       singleMetricParam = singleMetricAlgo.makeInitParams(params.getSelectorPlus(), params.getCursor());
       singleMetricAlgo.run(
diff --git a/processing/src/main/java/org/apache/druid/query/topn/InvertedTopNMetricSpec.java b/processing/src/main/java/org/apache/druid/query/topn/InvertedTopNMetricSpec.java
index b4c8cbc5f58..eac69d32837 100644
--- a/processing/src/main/java/org/apache/druid/query/topn/InvertedTopNMetricSpec.java
+++ b/processing/src/main/java/org/apache/druid/query/topn/InvertedTopNMetricSpec.java
@@ -21,7 +21,6 @@ package org.apache.druid.query.topn;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
-import org.apache.druid.java.util.common.guava.Comparators;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.PostAggregator;
 import org.apache.druid.query.dimension.DimensionSpec;
@@ -67,23 +66,7 @@ public class InvertedTopNMetricSpec implements TopNMetricSpec
       final List<PostAggregator> postAggregatorSpecs
   )
   {
-    return Comparators.inverse(
-        new Comparator()
-        {
-          @Override
-          public int compare(Object o1, Object o2)
-          {
-            // nulls last
-            if (o1 == null) {
-              return 1;
-            }
-            if (o2 == null) {
-              return -1;
-            }
-            return delegate.getComparator(aggregatorSpecs, postAggregatorSpecs).compare(o1, o2);
-          }
-        }
-    );
+    return Comparator.nullsFirst(delegate.getComparator(aggregatorSpecs, postAggregatorSpecs).reversed());
   }
 
   @Override
diff --git a/processing/src/main/java/org/apache/druid/segment/IndexIO.java b/processing/src/main/java/org/apache/druid/segment/IndexIO.java
index 1ee8b7c21e9..2293991c551 100644
--- a/processing/src/main/java/org/apache/druid/segment/IndexIO.java
+++ b/processing/src/main/java/org/apache/druid/segment/IndexIO.java
@@ -78,7 +78,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.TreeSet;
 
 public class IndexIO
 {
@@ -484,14 +483,6 @@ public class IndexIO
         }
       }
 
-      Set<String> colSet = new TreeSet<>();
-      for (String dimension : index.getAvailableDimensions()) {
-        colSet.add(dimension);
-      }
-      for (String metric : index.getAvailableMetrics()) {
-        colSet.add(metric);
-      }
-
       columns.put(
           ColumnHolder.TIME_COLUMN_NAME,
           new ColumnBuilder()
diff --git a/processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarLongsSerializer.java b/processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarLongsSerializer.java
index 8aadff24a7a..c1851c73d38 100644
--- a/processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarLongsSerializer.java
+++ b/processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarLongsSerializer.java
@@ -47,7 +47,7 @@ public class BlockLayoutColumnarLongsSerializer implements ColumnarLongsSerializ
   private int numInserted = 0;
   private int numInsertedForNextFlush;
 
-  private ByteBuffer endBuffer = null;
+  private ByteBuffer endBuffer;
 
   BlockLayoutColumnarLongsSerializer(
       SegmentWriteOutMedium segmentWriteOutMedium,
diff --git a/processing/src/main/java/org/apache/druid/segment/filter/Filters.java b/processing/src/main/java/org/apache/druid/segment/filter/Filters.java
index c9630ccecc8..a81eb60a8fe 100644
--- a/processing/src/main/java/org/apache/druid/segment/filter/Filters.java
+++ b/processing/src/main/java/org/apache/druid/segment/filter/Filters.java
@@ -397,7 +397,7 @@ public class Filters
         {
           private final int bitmapIndexCardinality = bitmapIndex.getCardinality();
           private int nextIndex = 0;
-          private int found = -1;
+          private int found;
 
           {
             found = findNextIndex();
diff --git a/processing/src/main/java/org/apache/druid/segment/filter/LikeFilter.java b/processing/src/main/java/org/apache/druid/segment/filter/LikeFilter.java
index 493eb9ec72b..018102a1833 100644
--- a/processing/src/main/java/org/apache/druid/segment/filter/LikeFilter.java
+++ b/processing/src/main/java/org/apache/druid/segment/filter/LikeFilter.java
@@ -174,7 +174,7 @@ public class LikeFilter implements Filter
         return new IntIterator()
         {
           int currIndex = startIndex;
-          int found = -1;
+          int found;
 
           {
             found = findNext();
diff --git a/processing/src/test/java/org/apache/druid/query/aggregation/JavaScriptAggregatorTest.java b/processing/src/test/java/org/apache/druid/query/aggregation/JavaScriptAggregatorTest.java
index 960b4701b42..757001b0ed3 100644
--- a/processing/src/test/java/org/apache/druid/query/aggregation/JavaScriptAggregatorTest.java
+++ b/processing/src/test/java/org/apache/druid/query/aggregation/JavaScriptAggregatorTest.java
@@ -322,7 +322,7 @@ public class JavaScriptAggregatorTest
 
     // warmup
     int i = 0;
-    long t = 0;
+    long t;
     while (i < 10000) {
       aggregate(selector, aggRhino);
       ++i;
diff --git a/processing/src/test/java/org/apache/druid/query/select/SelectBinaryFnTest.java b/processing/src/test/java/org/apache/druid/query/select/SelectBinaryFnTest.java
index 2de7b4f3bbb..219452e3b99 100644
--- a/processing/src/test/java/org/apache/druid/query/select/SelectBinaryFnTest.java
+++ b/processing/src/test/java/org/apache/druid/query/select/SelectBinaryFnTest.java
@@ -137,9 +137,6 @@ public class SelectBinaryFnTest
     Assert.assertEquals(res1.getTimestamp(), merged.getTimestamp());
 
     LinkedHashMap<String, Integer> expectedPageIds = Maps.newLinkedHashMap();
-    expectedPageIds.put(segmentId1, 0);
-    expectedPageIds.put(segmentId2, 0);
-    expectedPageIds.put(segmentId2, 1);
     expectedPageIds.put(segmentId1, 1);
     expectedPageIds.put(segmentId2, 2);
 
diff --git a/processing/src/test/java/org/apache/druid/query/timeboundary/TimeBoundaryQueryRunnerTest.java b/processing/src/test/java/org/apache/druid/query/timeboundary/TimeBoundaryQueryRunnerTest.java
index 06c7eaa2bb0..6527f3ceefd 100644
--- a/processing/src/test/java/org/apache/druid/query/timeboundary/TimeBoundaryQueryRunnerTest.java
+++ b/processing/src/test/java/org/apache/druid/query/timeboundary/TimeBoundaryQueryRunnerTest.java
@@ -24,7 +24,6 @@ import com.google.common.collect.Iterables;
 import com.google.common.io.CharSource;
 import org.apache.commons.lang.StringUtils;
 import org.apache.druid.java.util.common.DateTimes;
-import org.apache.druid.java.util.common.Intervals;
 import org.apache.druid.java.util.common.granularity.Granularities;
 import org.apache.druid.query.Druids;
 import org.apache.druid.query.QueryPlus;
@@ -40,7 +39,6 @@ import org.apache.druid.segment.TestIndex;
 import org.apache.druid.segment.incremental.IncrementalIndex;
 import org.apache.druid.segment.incremental.IncrementalIndexSchema;
 import org.apache.druid.timeline.DataSegment;
-import org.apache.druid.timeline.TimelineObjectHolder;
 import org.apache.druid.timeline.VersionedIntervalTimeline;
 import org.apache.druid.timeline.partition.NoneShardSpec;
 import org.apache.druid.timeline.partition.SingleElementPartitionChunk;
@@ -80,7 +78,6 @@ public class TimeBoundaryQueryRunnerTest
   );
   private static Segment segment0;
   private static Segment segment1;
-  private static List<String> segmentIdentifiers;
 
   public TimeBoundaryQueryRunnerTest(
       QueryRunner runner
@@ -157,11 +154,6 @@ public class TimeBoundaryQueryRunnerTest
     timeline.add(index0.getInterval(), "v1", new SingleElementPartitionChunk(segment0));
     timeline.add(index1.getInterval(), "v1", new SingleElementPartitionChunk(segment1));
 
-    segmentIdentifiers = new ArrayList<>();
-    for (TimelineObjectHolder<String, ?> holder : timeline.lookup(Intervals.of("2011-01-12/2011-01-17"))) {
-      segmentIdentifiers.add(makeIdentifier(holder.getInterval(), holder.getVersion()));
-    }
-
     return QueryRunnerTestHelper.makeFilteringQueryRunner(timeline, factory);
   }
 
diff --git a/processing/src/test/java/org/apache/druid/segment/SchemalessTestSimpleTest.java b/processing/src/test/java/org/apache/druid/segment/SchemalessTestSimpleTest.java
index b16157e369a..a6a2330774e 100644
--- a/processing/src/test/java/org/apache/druid/segment/SchemalessTestSimpleTest.java
+++ b/processing/src/test/java/org/apache/druid/segment/SchemalessTestSimpleTest.java
@@ -57,6 +57,7 @@ import org.apache.druid.query.topn.TopNQueryBuilder;
 import org.apache.druid.query.topn.TopNResultValue;
 import org.apache.druid.segment.incremental.IncrementalIndex;
 import org.apache.druid.segment.writeout.SegmentWriteOutMediumFactory;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
@@ -167,6 +168,7 @@ public class SchemalessTestSimpleTest
 
   //  @Test TODO: Handling of null values is inconsistent right now, need to make it all consistent and re-enable test
   // TODO: Complain to Eric when you see this.  It shouldn't be like this...
+  @Ignore
   @SuppressWarnings("unused")
   public void testFullOnTopN()
   {
diff --git a/server/src/main/java/org/apache/druid/client/cache/BytesBoundedLinkedQueue.java b/server/src/main/java/org/apache/druid/client/cache/BytesBoundedLinkedQueue.java
index f996d47ae00..25a2da4c899 100644
--- a/server/src/main/java/org/apache/druid/client/cache/BytesBoundedLinkedQueue.java
+++ b/server/src/main/java/org/apache/druid/client/cache/BytesBoundedLinkedQueue.java
@@ -137,7 +137,6 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
     checkNotNull(e);
     checkSize(e);
     long nanos = unit.toNanos(timeout);
-    boolean added = false;
     putLock.lockInterruptibly();
     try {
       while (currentSize.get() + getBytesSize(e) > capacity) {
@@ -148,16 +147,12 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
       }
       delegate.add(e);
       elementAdded(e);
-      added = true;
     }
     finally {
       putLock.unlock();
     }
-    if (added) {
-      signalNotEmpty();
-    }
-    return added;
-
+    signalNotEmpty();
+    return true;
   }
 
   @Override
@@ -222,12 +217,12 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
     if (c == this) {
       throw new IllegalArgumentException();
     }
-    int n = 0;
+    int n;
     takeLock.lock();
     try {
       // elementCount.get provides visibility to first n Nodes
       n = Math.min(maxElements, elementCount.get());
-      if (n < 0) {
+      if (n <= 0) {
         return 0;
       }
       for (int i = 0; i < n; i++) {
@@ -239,9 +234,7 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
     finally {
       takeLock.unlock();
     }
-    if (n > 0) {
-      signalNotFull();
-    }
+    signalNotFull();
     return n;
   }
 
@@ -250,7 +243,7 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
   {
     checkNotNull(e);
     checkSize(e);
-    boolean added = false;
+    boolean added;
     putLock.lock();
     try {
       if (currentSize.get() + getBytesSize(e) > capacity) {
@@ -274,7 +267,7 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
   @Override
   public E poll()
   {
-    E e = null;
+    E e;
     takeLock.lock();
     try {
       e = delegate.poll();
@@ -295,7 +288,7 @@ public abstract class BytesBoundedLinkedQueue<E> extends AbstractQueue<E> implem
   public E poll(long timeout, TimeUnit unit) throws InterruptedException
   {
     long nanos = unit.toNanos(timeout);
-    E e = null;
+    E e;
     takeLock.lockInterruptibly();
     try {
       while (elementCount.get() == 0) {
diff --git a/server/src/main/java/org/apache/druid/metadata/SQLMetadataConnector.java b/server/src/main/java/org/apache/druid/metadata/SQLMetadataConnector.java
index ddd33d1b159..f7243751a9f 100644
--- a/server/src/main/java/org/apache/druid/metadata/SQLMetadataConnector.java
+++ b/server/src/main/java/org/apache/druid/metadata/SQLMetadataConnector.java
@@ -639,7 +639,7 @@ public abstract class SQLMetadataConnector implements MetadataStorageConnector
   {
     MetadataStorageConnectorConfig connectorConfig = getConfig();
 
-    BasicDataSource dataSource = null;
+    BasicDataSource dataSource;
 
     try {
       Properties dbcpProperties = connectorConfig.getDbcpProperties();
diff --git a/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java b/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java
index 9939fad7dae..94e2c6cd50b 100644
--- a/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java
+++ b/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java
@@ -242,7 +242,7 @@ public class EventReceiverFirehoseFactory implements FirehoseFactory<InputRowPar
       }
 
       CountingInputStream countingInputStream = new CountingInputStream(in);
-      Collection<Map<String, Object>> events = null;
+      Collection<Map<String, Object>> events;
       try {
         events = objectMapper.readValue(
             countingInputStream,
diff --git a/server/src/main/java/org/apache/druid/server/coordinator/ReplicationThrottler.java b/server/src/main/java/org/apache/druid/server/coordinator/ReplicationThrottler.java
index f9b4d7bf748..a08a68c76d0 100644
--- a/server/src/main/java/org/apache/druid/server/coordinator/ReplicationThrottler.java
+++ b/server/src/main/java/org/apache/druid/server/coordinator/ReplicationThrottler.java
@@ -154,7 +154,7 @@ public class ReplicationThrottler
         lifetime = maxLifetime;
         lifetimes.put(tier, lifetime);
       }
-      lifetimes.put(tier, --lifetime);
+      lifetimes.put(tier, lifetime - 1);
     }
 
     public void resetLifetime(String tier)
diff --git a/server/src/main/java/org/apache/druid/server/coordinator/SegmentReplicantLookup.java b/server/src/main/java/org/apache/druid/server/coordinator/SegmentReplicantLookup.java
index 145b69b57de..6c122870df4 100644
--- a/server/src/main/java/org/apache/druid/server/coordinator/SegmentReplicantLookup.java
+++ b/server/src/main/java/org/apache/druid/server/coordinator/SegmentReplicantLookup.java
@@ -47,7 +47,7 @@ public class SegmentReplicantLookup
           if (numReplicants == null) {
             numReplicants = 0;
           }
-          segmentsInCluster.put(segment.getIdentifier(), server.getTier(), ++numReplicants);
+          segmentsInCluster.put(segment.getIdentifier(), server.getTier(), numReplicants + 1);
         }
 
         // Also account for queued segments
@@ -56,7 +56,7 @@ public class SegmentReplicantLookup
           if (numReplicants == null) {
             numReplicants = 0;
           }
-          loadingSegments.put(segment.getIdentifier(), server.getTier(), ++numReplicants);
+          loadingSegments.put(segment.getIdentifier(), server.getTier(), numReplicants + 1);
         }
       }
     }
diff --git a/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java b/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java
index 793e19d0add..77ca931eae1 100644
--- a/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java
+++ b/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java
@@ -276,7 +276,7 @@ public class DatasourcesResource
       return Response.noContent().build();
     }
 
-    final Comparator<Interval> comparator = Comparators.inverse(Comparators.intervalsByStartThenEnd());
+    final Comparator<Interval> comparator = Comparators.intervalsByStartThenEnd().reversed();
 
     if (full != null) {
       final Map<Interval, Map<String, Object>> retVal = new TreeMap<>(comparator);
@@ -342,7 +342,7 @@ public class DatasourcesResource
       return Response.noContent().build();
     }
 
-    final Comparator<Interval> comparator = Comparators.inverse(Comparators.intervalsByStartThenEnd());
+    final Comparator<Interval> comparator = Comparators.intervalsByStartThenEnd().reversed();
     if (full != null) {
       final Map<Interval, Map<String, Object>> retVal = new TreeMap<>(comparator);
       for (DataSegment dataSegment : dataSource.getSegments()) {
@@ -385,7 +385,7 @@ public class DatasourcesResource
       return Response.ok(retVal).build();
     }
 
-    final Set<String> retVal = new TreeSet<>(Comparators.inverse(String.CASE_INSENSITIVE_ORDER));
+    final Set<String> retVal = new TreeSet<>(String.CASE_INSENSITIVE_ORDER.reversed());
     for (DataSegment dataSegment : dataSource.getSegments()) {
       if (theInterval.contains(dataSegment.getInterval())) {
         retVal.add(dataSegment.getIdentifier());
diff --git a/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java b/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java
index 29d92f09826..56357944c5f 100644
--- a/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java
+++ b/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java
@@ -70,7 +70,7 @@ public class IntervalsResource
   @Produces(MediaType.APPLICATION_JSON)
   public Response getIntervals(@Context final HttpServletRequest req)
   {
-    final Comparator<Interval> comparator = Comparators.inverse(Comparators.intervalsByStartThenEnd());
+    final Comparator<Interval> comparator = Comparators.intervalsByStartThenEnd().reversed();
     final Set<ImmutableDruidDataSource> datasources = InventoryViewUtils.getSecuredDataSources(
         req,
         serverInventoryView,
@@ -80,11 +80,7 @@ public class IntervalsResource
     final Map<Interval, Map<String, Map<String, Object>>> retVal = new TreeMap<>(comparator);
     for (ImmutableDruidDataSource dataSource : datasources) {
       for (DataSegment dataSegment : dataSource.getSegments()) {
-        Map<String, Map<String, Object>> interval = retVal.get(dataSegment.getInterval());
-        if (interval == null) {
-          Map<String, Map<String, Object>> tmp = new HashMap<>();
-          retVal.put(dataSegment.getInterval(), tmp);
-        }
+        retVal.computeIfAbsent(dataSegment.getInterval(), i -> new HashMap<>());
         setProperties(retVal, dataSource, dataSegment);
       }
     }
@@ -109,18 +105,14 @@ public class IntervalsResource
         authorizerMapper
     );
 
-    final Comparator<Interval> comparator = Comparators.inverse(Comparators.intervalsByStartThenEnd());
+    final Comparator<Interval> comparator = Comparators.intervalsByStartThenEnd().reversed();
 
     if (full != null) {
       final Map<Interval, Map<String, Map<String, Object>>> retVal = new TreeMap<>(comparator);
       for (ImmutableDruidDataSource dataSource : datasources) {
         for (DataSegment dataSegment : dataSource.getSegments()) {
           if (theInterval.contains(dataSegment.getInterval())) {
-            Map<String, Map<String, Object>> dataSourceInterval = retVal.get(dataSegment.getInterval());
-            if (dataSourceInterval == null) {
-              Map<String, Map<String, Object>> tmp = new HashMap<>();
-              retVal.put(dataSegment.getInterval(), tmp);
-            }
+            retVal.computeIfAbsent(dataSegment.getInterval(), k -> new HashMap<>());
             setProperties(retVal, dataSource, dataSegment);
           }
         }
diff --git a/server/src/main/java/org/apache/druid/server/http/LookupCoordinatorResource.java b/server/src/main/java/org/apache/druid/server/http/LookupCoordinatorResource.java
index 881f3e53e05..90e56941ce7 100644
--- a/server/src/main/java/org/apache/druid/server/http/LookupCoordinatorResource.java
+++ b/server/src/main/java/org/apache/druid/server/http/LookupCoordinatorResource.java
@@ -482,7 +482,7 @@ public class LookupCoordinatorResource
   )
   {
     try {
-      Collection<String> tiers = null;
+      Collection<String> tiers;
       if (discover) {
         tiers = lookupCoordinatorManager.discoverTiers();
       } else {
diff --git a/server/src/main/java/org/apache/druid/server/initialization/jetty/JettyServerInitUtils.java b/server/src/main/java/org/apache/druid/server/initialization/jetty/JettyServerInitUtils.java
index 90e9d614592..0b0234324a8 100644
--- a/server/src/main/java/org/apache/druid/server/initialization/jetty/JettyServerInitUtils.java
+++ b/server/src/main/java/org/apache/druid/server/initialization/jetty/JettyServerInitUtils.java
@@ -57,7 +57,7 @@ public class JettyServerInitUtils
     for (ServletFilterHolder servletFilterHolder : extensionFilters) {
       // Check the Filter first to guard against people who don't read the docs and return the Class even
       // when they have an instance.
-      FilterHolder holder = null;
+      FilterHolder holder;
       if (servletFilterHolder.getFilter() != null) {
         holder = new FilterHolder(servletFilterHolder.getFilter());
       } else if (servletFilterHolder.getFilterClass() != null) {
diff --git a/server/src/main/java/org/apache/druid/server/security/PreResponseAuthorizationCheckFilter.java b/server/src/main/java/org/apache/druid/server/security/PreResponseAuthorizationCheckFilter.java
index f88edada1e1..9b72b19e36e 100644
--- a/server/src/main/java/org/apache/druid/server/security/PreResponseAuthorizationCheckFilter.java
+++ b/server/src/main/java/org/apache/druid/server/security/PreResponseAuthorizationCheckFilter.java
@@ -24,7 +24,6 @@ import org.apache.druid.java.util.common.ISE;
 import org.apache.druid.java.util.emitter.EmittingLogger;
 import org.apache.druid.query.QueryInterruptedException;
 import org.apache.druid.server.DruidNode;
-import org.eclipse.jetty.server.Response;
 
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
@@ -94,7 +93,7 @@ public class PreResponseAuthorizationCheckFilter implements Filter
       );
     }
 
-    if (authInfoChecked != null && !authInfoChecked && response.getStatus() != Response.SC_FORBIDDEN) {
+    if (authInfoChecked != null && !authInfoChecked && response.getStatus() != HttpServletResponse.SC_FORBIDDEN) {
       handleAuthorizationCheckError(
           "Request's authorization check failed but status code was not 403.",
           request,
@@ -134,7 +133,7 @@ public class PreResponseAuthorizationCheckFilter implements Filter
     );
     unauthorizedError.setStackTrace(new StackTraceElement[0]);
     OutputStream out = response.getOutputStream();
-    sendJsonError(response, Response.SC_UNAUTHORIZED, jsonMapper.writeValueAsString(unauthorizedError), out);
+    sendJsonError(response, HttpServletResponse.SC_UNAUTHORIZED, jsonMapper.writeValueAsString(unauthorizedError), out);
     out.close();
     return;
   }
@@ -157,7 +156,7 @@ public class PreResponseAuthorizationCheckFilter implements Filter
       throw new ISE(errorMsg);
     } else {
       try {
-        servletResponse.sendError(Response.SC_FORBIDDEN);
+        servletResponse.sendError(HttpServletResponse.SC_FORBIDDEN);
       }
       catch (Exception e) {
         throw new RuntimeException(e);
diff --git a/server/src/main/java/org/apache/druid/server/security/SecuritySanityCheckFilter.java b/server/src/main/java/org/apache/druid/server/security/SecuritySanityCheckFilter.java
index be71e4631c1..f222e5a8a6f 100644
--- a/server/src/main/java/org/apache/druid/server/security/SecuritySanityCheckFilter.java
+++ b/server/src/main/java/org/apache/druid/server/security/SecuritySanityCheckFilter.java
@@ -23,7 +23,6 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.query.QueryInterruptedException;
 import org.apache.druid.server.DruidNode;
-import org.eclipse.jetty.server.Response;
 
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
@@ -79,7 +78,7 @@ public class SecuritySanityCheckFilter implements Filter
 
     AuthenticationResult result = (AuthenticationResult) request.getAttribute(AuthConfig.DRUID_AUTHENTICATION_RESULT);
     if (authInfoChecked != null || result != null || allowUnsecured != null) {
-      sendJsonError(httpResponse, Response.SC_FORBIDDEN, unauthorizedMessage, out);
+      sendJsonError(httpResponse, HttpServletResponse.SC_FORBIDDEN, unauthorizedMessage, out);
       out.close();
       return;
     }
diff --git a/server/src/test/java/org/apache/druid/client/CachingClusteredClientTest.java b/server/src/test/java/org/apache/druid/client/CachingClusteredClientTest.java
index d5bd504191a..f65dc3070d8 100644
--- a/server/src/test/java/org/apache/druid/client/CachingClusteredClientTest.java
+++ b/server/src/test/java/org/apache/druid/client/CachingClusteredClientTest.java
@@ -2875,6 +2875,9 @@ public class CachingClusteredClientTest
       @Override
       public boolean equals(Object o)
       {
+        if (!(o instanceof DataSegment)) {
+          return false;
+        }
         return baseSegment.equals(o);
       }
 
diff --git a/server/src/test/java/org/apache/druid/client/cache/BytesBoundedLinkedQueueTest.java b/server/src/test/java/org/apache/druid/client/cache/BytesBoundedLinkedQueueTest.java
index 940160cce3c..b01ad799311 100644
--- a/server/src/test/java/org/apache/druid/client/cache/BytesBoundedLinkedQueueTest.java
+++ b/server/src/test/java/org/apache/druid/client/cache/BytesBoundedLinkedQueueTest.java
@@ -183,7 +183,7 @@ public class BytesBoundedLinkedQueueTest
     Assert.assertFalse(q.offer(new TestObject(2), delayMS, TimeUnit.MILLISECONDS));
   }
 
- // @Test
+  @Test
   public void testConcurrentOperations() throws Exception
   {
     final BlockingQueue<TestObject> q = getQueue(Integer.MAX_VALUE);
@@ -240,8 +240,7 @@ public class BytesBoundedLinkedQueueTest
                 public Boolean call()
                 {
                   while (!stopTest.get()) {
-                    System.out
-                          .println("drained elements : " + q.drainTo(new ArrayList<TestObject>(), Integer.MAX_VALUE));
+                    q.drainTo(new ArrayList<>(), Integer.MAX_VALUE);
                   }
                   return true;
                 }
diff --git a/server/src/test/java/org/apache/druid/client/cache/HybridCacheTest.java b/server/src/test/java/org/apache/druid/client/cache/HybridCacheTest.java
index 4284bd535b4..b5d96ebe2c2 100644
--- a/server/src/test/java/org/apache/druid/client/cache/HybridCacheTest.java
+++ b/server/src/test/java/org/apache/druid/client/cache/HybridCacheTest.java
@@ -172,8 +172,8 @@ public class HybridCacheTest
       Assert.assertEquals(Sets.newHashSet(key3), res.keySet());
       Assert.assertArrayEquals(value3, res.get(key3));
 
-      Assert.assertEquals(++hits, cache.getStats().getNumHits());
-      Assert.assertEquals(++misses, cache.getStats().getNumMisses());
+      Assert.assertEquals(hits + 1, cache.getStats().getNumHits());
+      Assert.assertEquals(misses + 1, cache.getStats().getNumMisses());
     }
   }
 }
diff --git a/server/src/test/java/org/apache/druid/client/cache/MemcachedCacheBenchmark.java b/server/src/test/java/org/apache/druid/client/cache/MemcachedCacheBenchmark.java
index 313ecdfd35a..fda0b64c414 100644
--- a/server/src/test/java/org/apache/druid/client/cache/MemcachedCacheBenchmark.java
+++ b/server/src/test/java/org/apache/druid/client/cache/MemcachedCacheBenchmark.java
@@ -131,7 +131,7 @@ public class MemcachedCacheBenchmark extends SimpleBenchmark
 
   public long timeGetObject(int reps)
   {
-    byte[] bytes = null;
+    byte[] bytes;
     long count = 0;
     for (int i = 0; i < reps; i++) {
       for (int k = 0; k < objectCount; ++k) {
diff --git a/server/src/test/java/org/apache/druid/segment/realtime/appenderator/AppenderatorPlumberTest.java b/server/src/test/java/org/apache/druid/segment/realtime/appenderator/AppenderatorPlumberTest.java
index d87841293b2..b5f37a6cca3 100644
--- a/server/src/test/java/org/apache/druid/segment/realtime/appenderator/AppenderatorPlumberTest.java
+++ b/server/src/test/java/org/apache/druid/segment/realtime/appenderator/AppenderatorPlumberTest.java
@@ -30,9 +30,6 @@ import org.easymock.EasyMock;
 import org.junit.Assert;
 import org.junit.Test;
 
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-
 public class AppenderatorPlumberTest
 {
   private final AppenderatorPlumber plumber;
@@ -94,43 +91,29 @@ public class AppenderatorPlumberTest
   @Test
   public void testSimpleIngestion() throws Exception
   {
-
-    final ConcurrentMap<String, String> commitMetadata = new ConcurrentHashMap<>();    
-    
     Appenderator appenderator = appenderatorTester.getAppenderator();
 
     // startJob
     Assert.assertEquals(null, plumber.startJob());
 
     // getDataSource
-    Assert.assertEquals(AppenderatorTester.DATASOURCE,
-        appenderator.getDataSource());
+    Assert.assertEquals(AppenderatorTester.DATASOURCE, appenderator.getDataSource());
 
     InputRow[] rows = new InputRow[] {AppenderatorTest.IR("2000", "foo", 1), 
         AppenderatorTest.IR("2000", "bar", 2), AppenderatorTest.IR("2000", "qux", 4)};
     // add
-    commitMetadata.put("x", "1");
-    Assert.assertEquals(
-        1,
-        plumber.add(rows[0], null).getRowCount());
+    Assert.assertEquals(1, plumber.add(rows[0], null).getRowCount());
 
-    commitMetadata.put("x", "2");
-    Assert.assertEquals(
-        2,
-        plumber.add(rows[1], null).getRowCount());
+    Assert.assertEquals(2, plumber.add(rows[1], null).getRowCount());
 
-    commitMetadata.put("x", "3");
-    Assert.assertEquals(
-        3,
-        plumber.add(rows[2], null).getRowCount());
+    Assert.assertEquals(3, plumber.add(rows[2], null).getRowCount());
 
     
     Assert.assertEquals(1, plumber.getSegmentsView().size());
     
     SegmentIdentifier si = plumber.getSegmentsView().values().toArray(new SegmentIdentifier[0])[0];
     
-    Assert.assertEquals(3,
-        appenderator.getRowCount(si));
+    Assert.assertEquals(3, appenderator.getRowCount(si));
 
     appenderator.clear();    
     Assert.assertTrue(appenderator.getSegments().isEmpty());
diff --git a/server/src/test/java/org/apache/druid/server/coordinator/CuratorDruidCoordinatorTest.java b/server/src/test/java/org/apache/druid/server/coordinator/CuratorDruidCoordinatorTest.java
index 9312e4bed00..2b4a8c5c75e 100644
--- a/server/src/test/java/org/apache/druid/server/coordinator/CuratorDruidCoordinatorTest.java
+++ b/server/src/test/java/org/apache/druid/server/coordinator/CuratorDruidCoordinatorTest.java
@@ -307,14 +307,13 @@ public class CuratorDruidCoordinatorTest extends CuratorTestBase
     DataSegment segmentToMove = sourceSegments.get(2);
 
     List<String> sourceSegKeys = new ArrayList<>();
-    List<String> destSegKeys = new ArrayList<>();
 
     for (DataSegment segment : sourceSegments) {
       sourceSegKeys.add(announceBatchSegmentsForServer(source, ImmutableSet.of(segment), zkPathsConfig, jsonMapper));
     }
 
     for (DataSegment segment : destinationSegments) {
-      destSegKeys.add(announceBatchSegmentsForServer(dest, ImmutableSet.of(segment), zkPathsConfig, jsonMapper));
+      announceBatchSegmentsForServer(dest, ImmutableSet.of(segment), zkPathsConfig, jsonMapper);
     }
 
     Assert.assertTrue(timing.forWaiting().awaitLatch(segmentViewInitLatch));
diff --git a/server/src/test/java/org/apache/druid/server/router/JavaScriptTieredBrokerSelectorStrategyTest.java b/server/src/test/java/org/apache/druid/server/router/JavaScriptTieredBrokerSelectorStrategyTest.java
index 5db4b8f541b..277f56d6d83 100644
--- a/server/src/test/java/org/apache/druid/server/router/JavaScriptTieredBrokerSelectorStrategyTest.java
+++ b/server/src/test/java/org/apache/druid/server/router/JavaScriptTieredBrokerSelectorStrategyTest.java
@@ -94,7 +94,6 @@ public class JavaScriptTieredBrokerSelectorStrategyTest
   public void testGetBrokerServiceName()
   {
     final LinkedHashMap<String, String> tierBrokerMap = new LinkedHashMap<>();
-    tierBrokerMap.put("fast", "druid/fastBroker");
     tierBrokerMap.put("fast", "druid/broker");
     tierBrokerMap.put("slow", "druid/slowBroker");
 
diff --git a/services/src/main/java/org/apache/druid/cli/CoordinatorJettyServerInitializer.java b/services/src/main/java/org/apache/druid/cli/CoordinatorJettyServerInitializer.java
index dac70890a5a..64deddd89ce 100644
--- a/services/src/main/java/org/apache/druid/cli/CoordinatorJettyServerInitializer.java
+++ b/services/src/main/java/org/apache/druid/cli/CoordinatorJettyServerInitializer.java
@@ -117,7 +117,6 @@ class CoordinatorJettyServerInitializer implements JettyServerInitializer
     final ObjectMapper jsonMapper = injector.getInstance(Key.get(ObjectMapper.class, Json.class));
     final AuthenticatorMapper authenticatorMapper = injector.getInstance(AuthenticatorMapper.class);
 
-    List<Authenticator> authenticators = null;
     AuthenticationUtils.addSecuritySanityCheckFilter(root, jsonMapper);
 
     // perform no-op authorization for these resources
@@ -128,7 +127,7 @@ class CoordinatorJettyServerInitializer implements JettyServerInitializer
       AuthenticationUtils.addNoopAuthorizationFilters(root, CliOverlord.UNSECURED_PATHS);
     }
 
-    authenticators = authenticatorMapper.getAuthenticatorChain();
+    List<Authenticator> authenticators = authenticatorMapper.getAuthenticatorChain();
     AuthenticationUtils.addAuthenticationFilterChain(root, authenticators);
 
     AuthenticationUtils.addAllowOptionsFilter(root, authConfig.isAllowUnauthenticatedHttpOptions());
diff --git a/services/src/main/java/org/apache/druid/cli/PullDependencies.java b/services/src/main/java/org/apache/druid/cli/PullDependencies.java
index 4df077b745b..885e100104a 100644
--- a/services/src/main/java/org/apache/druid/cli/PullDependencies.java
+++ b/services/src/main/java/org/apache/druid/cli/PullDependencies.java
@@ -73,6 +73,7 @@ public class PullDependencies implements Runnable
 {
   private static final Logger log = new Logger(PullDependencies.class);
 
+  @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
   private static final Set<String> exclusions = new HashSet<>(
       /*
 
diff --git a/services/src/main/java/org/apache/druid/cli/QueryJettyServerInitializer.java b/services/src/main/java/org/apache/druid/cli/QueryJettyServerInitializer.java
index 48d2962497f..2c9260241bc 100644
--- a/services/src/main/java/org/apache/druid/cli/QueryJettyServerInitializer.java
+++ b/services/src/main/java/org/apache/druid/cli/QueryJettyServerInitializer.java
@@ -93,14 +93,13 @@ public class QueryJettyServerInitializer implements JettyServerInitializer
     final ObjectMapper jsonMapper = injector.getInstance(Key.get(ObjectMapper.class, Json.class));
     final AuthenticatorMapper authenticatorMapper = injector.getInstance(AuthenticatorMapper.class);
 
-    List<Authenticator> authenticators = null;
     AuthenticationUtils.addSecuritySanityCheckFilter(root, jsonMapper);
 
     // perform no-op authorization for these resources
     AuthenticationUtils.addNoopAuthorizationFilters(root, UNSECURED_PATHS);
     AuthenticationUtils.addNoopAuthorizationFilters(root, authConfig.getUnsecuredPaths());
 
-    authenticators = authenticatorMapper.getAuthenticatorChain();
+    List<Authenticator> authenticators = authenticatorMapper.getAuthenticatorChain();
     AuthenticationUtils.addAuthenticationFilterChain(root, authenticators);
 
     AuthenticationUtils.addAllowOptionsFilter(root, authConfig.isAllowUnauthenticatedHttpOptions());
diff --git a/sql/src/main/java/org/apache/druid/sql/avatica/DruidConnection.java b/sql/src/main/java/org/apache/druid/sql/avatica/DruidConnection.java
index c6d17f1efa0..fb93a698cbb 100644
--- a/sql/src/main/java/org/apache/druid/sql/avatica/DruidConnection.java
+++ b/sql/src/main/java/org/apache/druid/sql/avatica/DruidConnection.java
@@ -20,7 +20,6 @@
 package org.apache.druid.sql.avatica;
 
 import com.google.common.base.Preconditions;
-import com.google.common.base.Predicate;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSortedMap;
@@ -29,7 +28,6 @@ import com.google.common.collect.Sets;
 import org.apache.druid.java.util.common.ISE;
 import org.apache.druid.java.util.common.logger.Logger;
 
-import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 import java.util.HashMap;
 import java.util.Map;
@@ -85,17 +83,9 @@ public class DruidConnection
 
       // remove sensitive fields from the context, only the connection's context needs to have authentication
       // credentials
-      Map<String, Object> sanitizedContext = new HashMap<>();
-      sanitizedContext = Maps.filterEntries(
+      Map<String, Object> sanitizedContext = Maps.filterEntries(
           context,
-          new Predicate<Map.Entry<String, Object>>()
-          {
-            @Override
-            public boolean apply(@Nullable Map.Entry<String, Object> input)
-            {
-              return !SENSITIVE_CONTEXT_FIELDS.contains(input.getKey());
-            }
-          }
+          e -> !SENSITIVE_CONTEXT_FIELDS.contains(e.getKey())
       );
 
       final DruidStatement statement = new DruidStatement(