fix NPE that can happen when merging all null nested v4 format columns (#14068)

processing/src/main/java/org/apache/druid/segment/nested/CompressedNestedDataComplexColumn.java

@@ -134,7 +134,7 @@ public abstract class CompressedNestedDataComplexColumn<TStringDictionary extend
       Supplier<TStringDictionary> stringDictionary,
       Supplier<FixedIndexed<Long>> longDictionarySupplier,
       Supplier<FixedIndexed<Double>> doubleDictionarySupplier,
-      Supplier<FrontCodedIntArrayIndexed> arrayDictionarySupplier,
+      @Nullable Supplier<FrontCodedIntArrayIndexed> arrayDictionarySupplier,
       SmooshedFileMapper fileMapper,
       BitmapSerdeFactory bitmapSerdeFactory,
       ByteOrder byteOrder,
@@ -220,6 +220,9 @@ public abstract class CompressedNestedDataComplexColumn<TStringDictionary extend
   @Override
   public Indexed<Object[]> getArrayDictionary()
   {
+    if (arrayDictionarySupplier == null) {
+      return Indexed.empty();
+    }
     Iterable<Object[]> arrays = () -> {
       final TStringDictionary stringDictionary = stringDictionarySupplier.get();
       final FixedIndexed<Long> longDictionary = longDictionarySupplier.get();

processing/src/test/java/org/apache/druid/query/NestedDataTestUtils.java

@@ -40,6 +40,7 @@ import org.apache.druid.java.util.common.parsers.JSONPathSpec;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.CountAggregatorFactory;
 import org.apache.druid.query.expression.TestExprMacroTable;
+import org.apache.druid.segment.AutoTypeColumnSchema;
 import org.apache.druid.segment.IncrementalIndexSegment;
 import org.apache.druid.segment.IndexBuilder;
 import org.apache.druid.segment.IndexSpec;
@@ -92,7 +93,7 @@ public class NestedDataTestUtils
                     .useSchemaDiscovery(true)
                     .build();
 
-  public static final DimensionsSpec TSV_SCHEMA =
+  public static final DimensionsSpec TSV_V4_SCHEMA =
       DimensionsSpec.builder()
                     .setDimensions(
                         Arrays.asList(
@@ -100,7 +101,22 @@ public class NestedDataTestUtils
                             new NestedDataDimensionSchema("nest_json"),
                             new NestedDataDimensionSchema("nester_json"),
                             new NestedDataDimensionSchema("variant_json"),
-                            new NestedDataDimensionSchema("list_json")
+                            new NestedDataDimensionSchema("list_json"),
+                            new NestedDataDimensionSchema("nonexistent")
+                        )
+                    )
+                    .build();
+
+  public static final DimensionsSpec TSV_SCHEMA =
+      DimensionsSpec.builder()
+                    .setDimensions(
+                        Arrays.asList(
+                            new AutoTypeColumnSchema("dim"),
+                            new AutoTypeColumnSchema("nest_json"),
+                            new AutoTypeColumnSchema("nester_json"),
+                            new AutoTypeColumnSchema("variant_json"),
+                            new AutoTypeColumnSchema("list_json"),
+                            new AutoTypeColumnSchema("nonexistent")
                         )
                     )
                     .build();
@@ -110,12 +126,6 @@ public class NestedDataTestUtils
       null
   );
 
-  public static final InputRowSchema SIMPLE_DATA_TSV_SCHEMA = new InputRowSchema(
-      TIMESTAMP_SPEC,
-      TSV_SCHEMA,
-      null
-  );
-
   public static DelimitedInputFormat SIMPLE_DATA_TSV_INPUT_FORMAT = new DelimitedInputFormat(
       Arrays.asList(
           "timestamp",
@@ -161,6 +171,22 @@ public class NestedDataTestUtils
         tempFolder,
         closer,
         Granularities.NONE,
+        TSV_SCHEMA,
+        true
+    );
+  }
+
+  public static List<Segment> createSimpleSegmentsTsvV4(
+      TemporaryFolder tempFolder,
+      Closer closer
+  )
+      throws Exception
+  {
+    return createSimpleNestedTestDataTsvSegments(
+        tempFolder,
+        closer,
+        Granularities.NONE,
+        TSV_V4_SCHEMA,
         true
     );
   }
@@ -169,6 +195,7 @@ public class NestedDataTestUtils
       TemporaryFolder tempFolder,
       Closer closer,
       Granularity granularity,
+      DimensionsSpec dimensionsSpec,
       boolean rollup
   ) throws Exception
   {
@@ -178,7 +205,7 @@ public class NestedDataTestUtils
         SIMPLE_DATA_TSV_FILE,
         SIMPLE_DATA_TSV_INPUT_FORMAT,
         TIMESTAMP_SPEC,
-        SIMPLE_DATA_TSV_SCHEMA.getDimensionsSpec(),
+        dimensionsSpec,
         SIMPLE_DATA_TSV_TRANSFORM,
         COUNT,
         granularity,

processing/src/test/java/org/apache/druid/query/scan/NestedDataScanQueryTest.java

@@ -262,6 +262,35 @@ public class NestedDataScanQueryTest extends InitializedNullHandlingTest
     Assert.assertEquals(resultsSegments.get(0).getEvents().toString(), resultsRealtime.get(0).getEvents().toString());
   }
 
+  @Test
+  public void testIngestAndScanSegmentsTsvV4() throws Exception
+  {
+    Query<ScanResultValue> scanQuery = Druids.newScanQueryBuilder()
+                                             .dataSource("test_datasource")
+                                             .intervals(
+                                                 new MultipleIntervalSegmentSpec(
+                                                     Collections.singletonList(Intervals.ETERNITY)
+                                                 )
+                                             )
+                                             .virtualColumns(
+                                                 new NestedFieldVirtualColumn("nest", "$.x", "x"),
+                                                 new NestedFieldVirtualColumn("nester", "$.x[0]", "x_0"),
+                                                 new NestedFieldVirtualColumn("nester", "$.y.c[1]", "y_c_1")
+                                             )
+                                             .resultFormat(ScanQuery.ResultFormat.RESULT_FORMAT_COMPACTED_LIST)
+                                             .limit(100)
+                                             .context(ImmutableMap.of())
+                                             .build();
+    List<Segment> segs = NestedDataTestUtils.createSimpleSegmentsTsvV4(tempFolder, closer);
+
+    final Sequence<ScanResultValue> seq = helper.runQueryOnSegmentsObjs(segs, scanQuery);
+
+    List<ScanResultValue> results = seq.toList();
+    Assert.assertEquals(1, results.size());
+    Assert.assertEquals(8, ((List) results.get(0).getEvents()).size());
+    logResults(results);
+  }
+
   @Test
   public void testIngestAndScanSegmentsTsv() throws Exception
   {