Remove and forbid use of the type-unsafe empty Collections fields

This commit removes and now forbids all uses of the type-unsafe empty
Collections fields Collections#EMPTY_LIST, Collections#EMPTY_MAP, and
Collections#EMPTY_SET. The type-safe methods Collections#emptyList,
Collections#emptyMap, and Collections#emptySet should be used instead.

buildSrc/src/main/resources/forbidden/all-signatures.txt

@@ -112,3 +112,7 @@ java.lang.System#setProperty(java.lang.String,java.lang.String)
 java.lang.System#clearProperty(java.lang.String)
 java.lang.System#getProperties() @ Use BootstrapInfo.getSystemProperties for a read-only view
 
+@defaultMessage Avoid unchecked warnings by using Collections#empty(List|Map|Set) methods
+java.util.Collections#EMPTY_LIST
+java.util.Collections#EMPTY_MAP
+java.util.Collections#EMPTY_SET

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataCreateIndexService.java

@@ -299,7 +299,7 @@ public class MetaDataCreateIndexService extends AbstractComponent {
                     // Set up everything, now locally create the index to see that things are ok, and apply
                     final IndexMetaData tmpImd = IndexMetaData.builder(request.index()).settings(actualIndexSettings).build();
                     // create the index here (on the master) to validate it can be created, as well as adding the mapping
-                    indicesService.createIndex(nodeServicesProvider, tmpImd, Collections.EMPTY_LIST);
+                    indicesService.createIndex(nodeServicesProvider, tmpImd, Collections.emptyList());
                     indexCreated = true;
                     // now add the mappings
                     IndexService indexService = indicesService.indexServiceSafe(request.index());

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexAliasesService.java

@@ -99,7 +99,7 @@ public class MetaDataIndexAliasesService extends AbstractComponent {
                                     if (indexService == null) {
                                         // temporarily create the index and add mappings so we can parse the filter
                                         try {
-                                            indexService = indicesService.createIndex(nodeServicesProvider, indexMetaData, Collections.EMPTY_LIST);
+                                            indexService = indicesService.createIndex(nodeServicesProvider, indexMetaData, Collections.emptyList());
                                             if (indexMetaData.getMappings().containsKey(MapperService.DEFAULT_MAPPING)) {
                                                 indexService.mapperService().merge(MapperService.DEFAULT_MAPPING, indexMetaData.getMappings().get(MapperService.DEFAULT_MAPPING).source(), false, false);
                                             }

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java

@@ -218,8 +218,8 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
         try {
             // We cannot instantiate real analysis server at this point because the node might not have
             // been started yet. However, we don't really need real analyzers at this stage - so we can fake it
-            IndexSettings indexSettings = new IndexSettings(indexMetaData, this.settings, Collections.EMPTY_LIST);
+            IndexSettings indexSettings = new IndexSettings(indexMetaData, this.settings, Collections.emptyList());
-            SimilarityService similarityService = new SimilarityService(indexSettings, Collections.EMPTY_MAP);
+            SimilarityService similarityService = new SimilarityService(indexSettings, Collections.emptyMap());
 
             try (AnalysisService analysisService = new FakeAnalysisService(indexSettings)) {
                 try (MapperService mapperService = new MapperService(indexSettings, analysisService, similarityService, mapperRegistry)) {
@@ -256,7 +256,7 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
         };
 
         public FakeAnalysisService(IndexSettings indexSettings) {
-            super(indexSettings, Collections.EMPTY_MAP, Collections.EMPTY_MAP, Collections.EMPTY_MAP, Collections.EMPTY_MAP);
+            super(indexSettings, Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap());
         }
 
         @Override

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataMappingService.java

@@ -219,7 +219,7 @@ public class MetaDataMappingService extends AbstractComponent {
                                 IndexService indexService;
                                 if (indicesService.hasIndex(index) == false) {
                                     indicesToClose.add(index);
-                                    indexService = indicesService.createIndex(nodeServicesProvider, indexMetaData, Collections.EMPTY_LIST);
+                                    indexService = indicesService.createIndex(nodeServicesProvider, indexMetaData, Collections.emptyList());
                                     // add mappings for all types, we need them for cross-type validation
                                     for (ObjectCursor<MappingMetaData> mapping : indexMetaData.getMappings().values()) {
                                         indexService.mapperService().merge(mapping.value.type(), mapping.value.source(), false, request.updateAllTypes());

core/src/main/java/org/elasticsearch/common/util/ExtensionPoint.java

@@ -123,7 +123,7 @@ public abstract class ExtensionPoint {
     public static final class SelectedType<T> extends ClassMap<T> {
 
         public SelectedType(String name, Class<T> extensionClass) {
-            super(name, extensionClass, Collections.EMPTY_SET);
+            super(name, extensionClass, Collections.emptySet());
         }
 
         /**

core/src/main/java/org/elasticsearch/gateway/TransportNodesListGatewayStartedShards.java

@@ -131,7 +131,7 @@ public class TransportNodesListGatewayStartedShards extends TransportNodesAction
                 if (metaData != null) {
                     ShardPath shardPath = null;
                     try {
-                        IndexSettings indexSettings = new IndexSettings(metaData, settings, Collections.EMPTY_LIST);
+                        IndexSettings indexSettings = new IndexSettings(metaData, settings, Collections.emptyList());
                         shardPath = ShardPath.loadShardPath(logger, nodeEnv, shardId, indexSettings);
                         if (shardPath == null) {
                             throw new IllegalStateException(shardId + " no shard path found");

core/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java

@@ -55,7 +55,7 @@ public final class AnalysisRegistry implements Closeable {
     private final Environment environemnt;
 
     public AnalysisRegistry(HunspellService hunspellService, Environment environment) {
-        this(hunspellService, environment, Collections.EMPTY_MAP, Collections.EMPTY_MAP, Collections.EMPTY_MAP, Collections.EMPTY_MAP);
+        this(hunspellService, environment, Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap());
     }
 
     public AnalysisRegistry(HunspellService hunspellService, Environment environment,

core/src/main/java/org/elasticsearch/index/translog/Translog.java

@@ -166,7 +166,7 @@ public class Translog extends AbstractIndexShardComponent implements IndexShardC
                 current = createWriter(checkpoint.generation + 1);
                 this.lastCommittedTranslogFileGeneration = translogGeneration.translogFileGeneration;
             } else {
-                this.recoveredTranslogs = Collections.EMPTY_LIST;
+                this.recoveredTranslogs = Collections.emptyList();
                 IOUtils.rm(location);
                 logger.debug("wipe translog location - creating new translog");
                 Files.createDirectories(location);
@@ -582,7 +582,7 @@ public class Translog extends AbstractIndexShardComponent implements IndexShardC
      * and updated with any future translog.
      */
     public static final class View implements Closeable {
-        public static final Translog.View EMPTY_VIEW = new View(Collections.EMPTY_LIST, null);
+        public static final Translog.View EMPTY_VIEW = new View(Collections.emptyList(), null);
 
         boolean closed;
         // last in this list is always FsTranslog.current

core/src/main/java/org/elasticsearch/indices/IndicesService.java

@@ -264,7 +264,7 @@ public class IndicesService extends AbstractLifecycleComponent<IndicesService> i
         }
         final String indexName = indexMetaData.getIndex();
         final Predicate<String> indexNameMatcher = (indexExpression) -> indexNameExpressionResolver.matchesIndex(indexName, indexExpression, clusterService.state());
-        final IndexSettings idxSettings = new IndexSettings(indexMetaData, this.settings, Collections.EMPTY_LIST, indexNameMatcher);
+        final IndexSettings idxSettings = new IndexSettings(indexMetaData, this.settings, Collections.emptyList(), indexNameMatcher);
         Index index = new Index(indexMetaData.getIndex());
         if (indices.containsKey(index.name())) {
             throw new IndexAlreadyExistsException(index);
@@ -562,7 +562,7 @@ public class IndicesService extends AbstractLifecycleComponent<IndicesService> i
         // play safe here and make sure that we take node level settings into account.
         // we might run on nodes where we use shard FS and then in the future don't delete
         // actual content.
-        return new IndexSettings(metaData, settings, Collections.EMPTY_LIST);
+        return new IndexSettings(metaData, settings, Collections.emptyList());
     }
 
     /**

core/src/main/java/org/elasticsearch/indices/cluster/IndicesClusterStateService.java

@@ -245,7 +245,7 @@ public class IndicesClusterStateService extends AbstractLifecycleComponent<Indic
             } else {
                 final IndexMetaData metaData = previousState.metaData().index(index);
                 assert metaData != null;
-                indexSettings = new IndexSettings(metaData, settings, Collections.EMPTY_LIST);
+                indexSettings = new IndexSettings(metaData, settings, Collections.emptyList());
                 indicesService.deleteClosedIndex("closed index no longer part of the metadata", metaData, event.state());
             }
             try {

core/src/main/java/org/elasticsearch/indices/store/TransportNodesListShardStoreMetaData.java

@@ -171,7 +171,7 @@ public class TransportNodesListShardStoreMetaData extends TransportNodesAction<T
             if (!storeType.contains("fs")) {
                 return new StoreFilesMetaData(false, shardId, Store.MetadataSnapshot.EMPTY);
             }
-            final IndexSettings indexSettings = indexService != null ? indexService.getIndexSettings() : new IndexSettings(metaData, settings, Collections.EMPTY_LIST);
+            final IndexSettings indexSettings = indexService != null ? indexService.getIndexSettings() : new IndexSettings(metaData, settings, Collections.emptyList());
             final ShardPath shardPath = ShardPath.loadShardPath(logger, nodeEnv, shardId, indexSettings);
             if (shardPath == null) {
                 return new StoreFilesMetaData(false, shardId, Store.MetadataSnapshot.EMPTY);

core/src/main/java/org/elasticsearch/percolator/PercolateContext.java

@@ -729,7 +729,7 @@ public class PercolateContext extends SearchContext {
 
     @Override
     public Set<String> getHeaders() {
-        return Collections.EMPTY_SET;
+        return Collections.emptySet();
     }
 
     @Override

core/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java

@@ -294,7 +294,7 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent<Rep
         if (readOnly()) {
             throw new RepositoryException(this.repositoryName, "cannot delete snapshot from a readonly repository");
         }
-        List<String> indices = Collections.EMPTY_LIST;
+        List<String> indices = Collections.emptyList();
         Snapshot snapshot = null;
         try {
             snapshot = readSnapshot(snapshotId);

core/src/main/java/org/elasticsearch/script/Template.java

@@ -121,12 +121,12 @@ public class Template extends Script {
 
     @SuppressWarnings("unchecked")
     public static Script parse(Map<String, Object> config, boolean removeMatchedEntries, ParseFieldMatcher parseFieldMatcher) {
-        return new TemplateParser(Collections.EMPTY_MAP, MustacheScriptEngineService.NAME).parse(config, removeMatchedEntries, parseFieldMatcher);
+        return new TemplateParser(Collections.emptyMap(), MustacheScriptEngineService.NAME).parse(config, removeMatchedEntries, parseFieldMatcher);
     }
 
     @SuppressWarnings("unchecked")
     public static Template parse(XContentParser parser, ParseFieldMatcher parseFieldMatcher) throws IOException {
-        return new TemplateParser(Collections.EMPTY_MAP, MustacheScriptEngineService.NAME).parse(parser, parseFieldMatcher);
+        return new TemplateParser(Collections.emptyMap(), MustacheScriptEngineService.NAME).parse(parser, parseFieldMatcher);
     }
 
     @Deprecated

core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/heuristics/SignificanceHeuristicStreams.java

@@ -31,7 +31,7 @@ import java.util.Map;
  */
 public class SignificanceHeuristicStreams {
 
-    private static Map<String, Stream> STREAMS = Collections.EMPTY_MAP;
+    private static Map<String, Stream> STREAMS = Collections.emptyMap();
 
     static {
         HashMap<String, Stream> map = new HashMap<>();

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/BucketMetricsPipelineAggregator.java

@@ -78,7 +78,7 @@ public abstract class BucketMetricsPipelineAggregator extends SiblingPipelineAgg
                 }
             }
         }
-        return buildAggregation(Collections.EMPTY_LIST, metaData());
+        return buildAggregation(Collections.emptyList(), metaData());
     }
 
     /**

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/max/MaxBucketPipelineAggregator.java

@@ -90,7 +90,7 @@ public class MaxBucketPipelineAggregator extends BucketMetricsPipelineAggregator
     @Override
     protected InternalAggregation buildAggregation(List<PipelineAggregator> pipelineAggregators, Map<String, Object> metadata) {
         String[] keys = maxBucketKeys.toArray(new String[maxBucketKeys.size()]);
-        return new InternalBucketMetricValue(name(), keys, maxValue, formatter, Collections.EMPTY_LIST, metaData());
+        return new InternalBucketMetricValue(name(), keys, maxValue, formatter, Collections.emptyList(), metaData());
     }
 
     public static class Factory extends PipelineAggregatorFactory {

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/min/MinBucketPipelineAggregator.java

@@ -91,7 +91,7 @@ public class MinBucketPipelineAggregator extends BucketMetricsPipelineAggregator
     protected InternalAggregation buildAggregation(java.util.List<PipelineAggregator> pipelineAggregators,
             java.util.Map<String, Object> metadata) {
         String[] keys = minBucketKeys.toArray(new String[minBucketKeys.size()]);
-        return new InternalBucketMetricValue(name(), keys, minValue, formatter, Collections.EMPTY_LIST, metaData());
+        return new InternalBucketMetricValue(name(), keys, minValue, formatter, Collections.emptyList(), metaData());
     };
 
     public static class Factory extends PipelineAggregatorFactory {

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/movavg/models/MovAvgModelStreams.java

@@ -32,7 +32,7 @@ import java.util.Map;
  */
 public class MovAvgModelStreams {
 
-    private static Map<String, Stream> STREAMS = Collections.EMPTY_MAP;
+    private static Map<String, Stream> STREAMS = Collections.emptyMap();
 
     static {
         HashMap<String, Stream> map = new HashMap<>();

core/src/main/java/org/elasticsearch/search/suggest/Suggesters.java

@@ -35,7 +35,7 @@ public final class Suggesters extends ExtensionPoint.ClassMap<Suggester> {
     private final Map<String, Suggester> parsers;
 
     public Suggesters() {
-        this(Collections.EMPTY_MAP);
+        this(Collections.emptyMap());
     }
 
     public Suggesters(Map<String, Suggester> suggesters) {

core/src/main/java/org/elasticsearch/search/suggest/completion/CompletionSuggestionContext.java

@@ -38,10 +38,10 @@ public class CompletionSuggestionContext extends SuggestionSearchContext.Suggest
     private CompletionFieldMapper.CompletionFieldType fieldType;
     private CompletionSuggestionBuilder.FuzzyOptionsBuilder fuzzyOptionsBuilder;
     private CompletionSuggestionBuilder.RegexOptionsBuilder regexOptionsBuilder;
-    private Map<String, List<ContextMapping.QueryContext>> queryContexts = Collections.EMPTY_MAP;
+    private Map<String, List<ContextMapping.QueryContext>> queryContexts = Collections.emptyMap();
     private final MapperService mapperService;
     private final IndexFieldDataService indexFieldDataService;
-    private Set<String> payloadFields = Collections.EMPTY_SET;
+    private Set<String> payloadFields = Collections.emptySet();
 
     CompletionSuggestionContext(Suggester suggester, MapperService mapperService, IndexFieldDataService indexFieldDataService) {
         super(suggester);

core/src/main/java/org/elasticsearch/snapshots/Snapshot.java

@@ -29,8 +29,6 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
-import static java.util.Collections.*;
-
 /**
  * Represent information about snapshot
  */
@@ -93,7 +91,7 @@ public class Snapshot implements Comparable<Snapshot>, ToXContent, FromXContentB
      * Special constructor for the prototype object
      */
     private Snapshot() {
-        this("", (List<String>) EMPTY_LIST, 0);
+        this("", Collections.emptyList(), 0);
     }
 
     private static SnapshotState snapshotState(String reason, List<SnapshotShardFailure> shardFailures) {

core/src/main/java/org/elasticsearch/transport/local/LocalTransport.java

@@ -154,7 +154,7 @@ public class LocalTransport extends AbstractLifecycleComponent<Transport> implem
 
     @Override
     public Map<String, BoundTransportAddress> profileBoundAddresses() {
-        return Collections.EMPTY_MAP;
+        return Collections.emptyMap();
     }
 
     @Override

core/src/test/java/org/elasticsearch/client/transport/FailAndRetryMockTransport.java

@@ -189,6 +189,6 @@ abstract class FailAndRetryMockTransport<Response extends TransportResponse> imp
 
     @Override
     public Map<String, BoundTransportAddress> profileBoundAddresses() {
-        return Collections.EMPTY_MAP;
+        return Collections.emptyMap();
     }
 }

core/src/test/java/org/elasticsearch/client/transport/TransportClientNodesServiceTests.java

@@ -63,7 +63,7 @@ public class TransportClientNodesServiceTests extends ESTestCase {
             transport = new FailAndRetryMockTransport<TestResponse>(getRandom()) {
                 @Override
                 public List<String> getLocalAddresses() {
-                    return Collections.EMPTY_LIST;
+                    return Collections.emptyList();
                 }
 
                 @Override

core/src/test/java/org/elasticsearch/index/IndexModuleTests.java

@@ -104,8 +104,8 @@ public class IndexModuleTests extends ESTestCase {
         Set<ScriptEngineService> scriptEngines = new HashSet<>();
         scriptEngines.add(new MustacheScriptEngineService(settings));
         scriptEngines.addAll(Arrays.asList(scriptEngineServices));
-        ScriptService scriptService = new ScriptService(settings, environment, scriptEngines, new ResourceWatcherService(settings, threadPool), new ScriptContextRegistry(Collections.EMPTY_LIST));
+        ScriptService scriptService = new ScriptService(settings, environment, scriptEngines, new ResourceWatcherService(settings, threadPool), new ScriptContextRegistry(Collections.emptyList()));
-        IndicesQueriesRegistry indicesQueriesRegistry = new IndicesQueriesRegistry(settings, Collections.EMPTY_SET, new NamedWriteableRegistry());
+        IndicesQueriesRegistry indicesQueriesRegistry = new IndicesQueriesRegistry(settings, Collections.emptySet(), new NamedWriteableRegistry());
         return new NodeServicesProvider(threadPool, indicesQueryCache, null, warmer, bigArrays, client, scriptService, indicesQueriesRegistry, indicesFieldDataCache, circuitBreakerService);
     }
 

core/src/test/java/org/elasticsearch/index/IndexSettingsTests.java

@@ -95,7 +95,7 @@ public class IndexSettingsTests extends ESTestCase {
     public void testSettingsConsistency() {
         Version version = VersionUtils.getPreviousVersion();
         IndexMetaData metaData = newIndexMeta("index", Settings.settingsBuilder().put(IndexMetaData.SETTING_VERSION_CREATED, version).build());
-        IndexSettings settings = new IndexSettings(metaData, Settings.EMPTY, Collections.EMPTY_LIST);
+        IndexSettings settings = new IndexSettings(metaData, Settings.EMPTY, Collections.emptyList());
         assertEquals(version, settings.getIndexVersionCreated());
         assertEquals("_na_", settings.getUUID());
         try {
@@ -106,7 +106,7 @@ public class IndexSettingsTests extends ESTestCase {
         }
 
         metaData = newIndexMeta("index", Settings.settingsBuilder().put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT).put(IndexMetaData.SETTING_INDEX_UUID, "0xdeadbeef").build());
-        settings = new IndexSettings(metaData, Settings.EMPTY, Collections.EMPTY_LIST);
+        settings = new IndexSettings(metaData, Settings.EMPTY, Collections.emptyList());
         try {
             settings.updateIndexMetaData(newIndexMeta("index", Settings.builder().put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT).put("index.test.setting.int", 42).build()));
             fail("uuid missing/change");

core/src/test/java/org/elasticsearch/index/analysis/AnalysisModuleTests.java

@@ -72,7 +72,7 @@ public class AnalysisModuleTests extends ModuleTestCase {
 
     public AnalysisRegistry getNewRegistry(Settings settings) {
        return new AnalysisRegistry(null, new Environment(settings),
-                Collections.EMPTY_MAP, Collections.singletonMap("myfilter", MyFilterTokenFilterFactory::new), Collections.EMPTY_MAP, Collections.EMPTY_MAP);
+                Collections.emptyMap(), Collections.singletonMap("myfilter", MyFilterTokenFilterFactory::new), Collections.emptyMap(), Collections.emptyMap());
     }
 
     private Settings loadFromClasspath(String path) {

core/src/test/java/org/elasticsearch/index/analysis/AnalysisTestsHelper.java

@@ -51,6 +51,6 @@ public class AnalysisTestsHelper {
         }
         IndexSettings idxSettings = IndexSettingsModule.newIndexSettings(index, settings);
         Environment environment = new Environment(settings);
-        return new AnalysisRegistry(new HunspellService(settings, environment, Collections.EMPTY_MAP), environment).build(idxSettings);
+        return new AnalysisRegistry(new HunspellService(settings, environment, Collections.emptyMap()), environment).build(idxSettings);
     }
 }

core/src/test/java/org/elasticsearch/index/analysis/CompoundAnalysisTests.java

@@ -52,7 +52,7 @@ public class CompoundAnalysisTests extends ESTestCase {
         Settings settings = getJsonSettings();
         IndexSettings idxSettings = IndexSettingsModule.newIndexSettings(index, settings);
         AnalysisService analysisService = new AnalysisRegistry(null, new Environment(settings),
-                Collections.EMPTY_MAP,Collections.singletonMap("myfilter", MyFilterTokenFilterFactory::new),Collections.EMPTY_MAP,Collections.EMPTY_MAP).build(idxSettings);
+                Collections.emptyMap(),Collections.singletonMap("myfilter", MyFilterTokenFilterFactory::new),Collections.emptyMap(),Collections.emptyMap()).build(idxSettings);
 
         TokenFilterFactory filterFactory = analysisService.tokenFilter("dict_dec");
         MatcherAssert.assertThat(filterFactory, instanceOf(DictionaryCompoundWordTokenFilterFactory.class));
@@ -71,7 +71,7 @@ public class CompoundAnalysisTests extends ESTestCase {
         Index index = new Index("test");
         IndexSettings idxSettings = IndexSettingsModule.newIndexSettings(index, settings);
         AnalysisService analysisService = new AnalysisRegistry(null, new Environment(settings),
-                Collections.EMPTY_MAP, Collections.singletonMap("myfilter", MyFilterTokenFilterFactory::new),Collections.EMPTY_MAP,Collections.EMPTY_MAP).build(idxSettings);
+                Collections.emptyMap(), Collections.singletonMap("myfilter", MyFilterTokenFilterFactory::new),Collections.emptyMap(),Collections.emptyMap()).build(idxSettings);
 
         Analyzer analyzer = analysisService.analyzer(analyzerName).analyzer();
 

core/src/test/java/org/elasticsearch/index/codec/CodecTests.java

@@ -108,7 +108,7 @@ public class CodecTests extends ESTestCase {
                 .put("path.home", createTempDir())
                 .build();
         IndexSettings settings = IndexSettingsModule.newIndexSettings(new Index("_na"), nodeSettings);
-        SimilarityService similarityService = new SimilarityService(settings, Collections.EMPTY_MAP);
+        SimilarityService similarityService = new SimilarityService(settings, Collections.emptyMap());
         AnalysisService analysisService = new AnalysisRegistry(null, new Environment(nodeSettings)).build(settings);
         MapperRegistry mapperRegistry = new MapperRegistry(Collections.emptyMap(), Collections.emptyMap());
         MapperService service = new MapperService(settings, analysisService, similarityService, mapperRegistry);

core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -1617,7 +1617,7 @@ public class InternalEngineTests extends ESTestCase {
         // now it should be OK.
         IndexSettings indexSettings = new IndexSettings(defaultSettings.getIndexMetaData(),
                 Settings.builder().put(defaultSettings.getSettings()).put(EngineConfig.INDEX_FORCE_NEW_TRANSLOG, true).build(),
-                Collections.EMPTY_LIST);
+                Collections.emptyList());
         engine = createEngine(indexSettings, store, primaryTranslogDir, new MergeSchedulerConfig(indexSettings), newMergePolicy());
     }
 
@@ -1901,8 +1901,8 @@ public class InternalEngineTests extends ESTestCase {
             RootObjectMapper.Builder rootBuilder = new RootObjectMapper.Builder("test");
             Index index = new Index(indexName);
             IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(index, settings);
-            AnalysisService analysisService = new AnalysisService(indexSettings, Collections.EMPTY_MAP, Collections.EMPTY_MAP, Collections.EMPTY_MAP, Collections.EMPTY_MAP);
+            AnalysisService analysisService = new AnalysisService(indexSettings, Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap());
-            SimilarityService similarityService = new SimilarityService(indexSettings, Collections.EMPTY_MAP);
+            SimilarityService similarityService = new SimilarityService(indexSettings, Collections.emptyMap());
             MapperRegistry mapperRegistry = new IndicesModule().getMapperRegistry();
             MapperService mapperService = new MapperService(indexSettings, analysisService, similarityService, mapperRegistry);
             DocumentMapper.Builder b = new DocumentMapper.Builder(settings, rootBuilder, mapperService);

core/src/test/java/org/elasticsearch/index/query/AbstractQueryTestCase.java

@@ -241,7 +241,7 @@ public abstract class AbstractQueryTestCase<QB extends AbstractQueryBuilder<QB>>
         ).createInjector();
         AnalysisService analysisService = new AnalysisRegistry(null, new Environment(settings)).build(idxSettings);
         ScriptService scriptService = injector.getInstance(ScriptService.class);
-        SimilarityService similarityService = new SimilarityService(idxSettings, Collections.EMPTY_MAP);
+        SimilarityService similarityService = new SimilarityService(idxSettings, Collections.emptyMap());
         MapperRegistry mapperRegistry = injector.getInstance(MapperRegistry.class);
         MapperService mapperService = new MapperService(idxSettings, analysisService, similarityService, mapperRegistry);
         indexFieldDataService = new IndexFieldDataService(idxSettings, injector.getInstance(IndicesFieldDataCache.class), injector.getInstance(CircuitBreakerService.class), mapperService);

core/src/test/java/org/elasticsearch/index/query/TemplateQueryParserTests.java

@@ -120,7 +120,7 @@ public class TemplateQueryParserTests extends ESTestCase {
 
         AnalysisService analysisService = new AnalysisRegistry(null, new Environment(settings)).build(idxSettings);
         ScriptService scriptService = injector.getInstance(ScriptService.class);
-        SimilarityService similarityService = new SimilarityService(idxSettings, Collections.EMPTY_MAP);
+        SimilarityService similarityService = new SimilarityService(idxSettings, Collections.emptyMap());
         MapperRegistry mapperRegistry = new IndicesModule().getMapperRegistry();
         MapperService mapperService = new MapperService(idxSettings, analysisService, similarityService, mapperRegistry);
         IndexFieldDataService indexFieldDataService =new IndexFieldDataService(idxSettings, injector.getInstance(IndicesFieldDataCache.class), injector.getInstance(CircuitBreakerService.class), mapperService);

core/src/test/java/org/elasticsearch/search/aggregations/bucket/significant/SignificanceHeuristicTests.java

@@ -103,13 +103,13 @@ public class SignificanceHeuristicTests extends ESTestCase {
         if (randomBoolean()) {
             buckets.add(new SignificantLongTerms.Bucket(1, 2, 3, 4, 123, InternalAggregations.EMPTY, null));
             sTerms[0] = new SignificantLongTerms(10, 20, "some_name", null, 1, 1, heuristic, buckets,
-                    Collections.EMPTY_LIST, null);
+                    Collections.emptyList(), null);
             sTerms[1] = new SignificantLongTerms();
         } else {
 
             BytesRef term = new BytesRef("someterm");
             buckets.add(new SignificantStringTerms.Bucket(term, 1, 2, 3, 4, InternalAggregations.EMPTY));
-            sTerms[0] = new SignificantStringTerms(10, 20, "some_name", 1, 1, heuristic, buckets, Collections.EMPTY_LIST,
+            sTerms[0] = new SignificantStringTerms(10, 20, "some_name", 1, 1, heuristic, buckets, Collections.emptyList(),
                     null);
             sTerms[1] = new SignificantStringTerms();
         }

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/GceComputeServiceImpl.java

@@ -79,14 +79,15 @@ public class GceComputeServiceImpl extends AbstractLifecycleComponent<GceCompute
                         return list.execute();
                     }
                 });
-                if (instanceList.isEmpty()) {
+                // assist type inference
-                    return Collections.EMPTY_LIST;
+                List<Instance> items = instanceList.isEmpty() ? Collections.emptyList() : instanceList.getItems();
-                }
+                return items;
-                return instanceList.getItems();
             } catch (PrivilegedActionException e) {
                 logger.warn("Problem fetching instance list for zone {}", zoneId);
                 logger.debug("Full exception:", e);
-                return Collections.EMPTY_LIST;
+                // assist type inference
+                List<Instance> items = Collections.emptyList();
+                return items;
             }
         }).reduce(new ArrayList<>(), (a, b) -> {
             a.addAll(b);

test-framework/src/main/java/org/elasticsearch/test/IndexSettingsModule.java

@@ -54,6 +54,6 @@ public class IndexSettingsModule extends AbstractModule {
                 .put(settings)
                 .build();
         IndexMetaData metaData = IndexMetaData.builder(index.getName()).settings(build).build();
-        return new IndexSettings(metaData, Settings.EMPTY, Collections.EMPTY_LIST);
+        return new IndexSettings(metaData, Settings.EMPTY, Collections.emptyList());
     }
 }

test-framework/src/main/java/org/elasticsearch/test/TestSearchContext.java

@@ -650,7 +650,7 @@ public class TestSearchContext extends SearchContext {
 
     @Override
     public Set<String> getHeaders() {
-        return Collections.EMPTY_SET;
+        return Collections.emptySet();
     }
 
     @Override

test-framework/src/main/java/org/elasticsearch/test/store/MockFSDirectoryService.java

@@ -173,7 +173,7 @@ public class MockFSDirectoryService extends FsDirectoryService {
     private FsDirectoryService randomDirectorService(IndexStore indexStore, ShardPath path) {
         final IndexSettings indexSettings = indexStore.getIndexSettings();
         final IndexMetaData build = IndexMetaData.builder(indexSettings.getIndexMetaData()).settings(Settings.builder().put(indexSettings.getSettings()).put(IndexModule.STORE_TYPE, RandomPicks.randomFrom(random, IndexModule.Type.values()).getSettingsKey())).build();
-        final IndexSettings newIndexSettings = new IndexSettings(build, indexSettings.getNodeSettings(), Collections.EMPTY_LIST);
+        final IndexSettings newIndexSettings = new IndexSettings(build, indexSettings.getNodeSettings(), Collections.emptyList());
         return new FsDirectoryService(newIndexSettings, indexStore, path);
     }
 

test-framework/src/main/java/org/elasticsearch/test/transport/CapturingTransport.java

@@ -178,6 +178,6 @@ public class CapturingTransport implements Transport {
 
     @Override
     public List<String> getLocalAddresses() {
-        return Collections.EMPTY_LIST;
+        return Collections.emptyList();
     }
 }