Handling null operand in JSON_QUERY_ARRAY (#16118)

* fix return type inference for JSON_QUERY_ARRAY to be nullable

sql/src/main/java/org/apache/druid/sql/calcite/expression/builtin/NestedDataOperatorConversions.java

@@ -253,7 +253,7 @@ public class NestedDataOperatorConversions
                 SqlTypeFamily.CHARACTER
             )
         )
-        .returnTypeInference(NESTED_ARRAY_RETURN_TYPE_INFERENCE)
+        .returnTypeInference(NESTED_ARRAY_RETURN_TYPE_INFERENCE.andThen(SqlTypeTransforms.FORCE_NULLABLE))
         .functionCategory(SqlFunctionCategory.SYSTEM)
         .build();
 

sql/src/test/java/org/apache/druid/sql/calcite/CalciteNestedDataQueryTest.java

@@ -6626,6 +6626,46 @@ public class CalciteNestedDataQueryTest extends BaseCalciteQueryTest
         .run();
   }
 
+  @Test
+  public void testJsonQueryArrayNullArray()
+  {
+    cannotVectorize();
+    testBuilder()
+        .sql("SELECT JSON_QUERY_ARRAY(arrayObject, '$.') FROM druid.arrays where arrayObject is null limit 1")
+        .queryContext(QUERY_CONTEXT_DEFAULT)
+        .expectedQueries(
+            ImmutableList.of(
+                Druids.newScanQueryBuilder()
+                      .dataSource(DATA_SOURCE_ARRAYS)
+                      .intervals(querySegmentSpec(Filtration.eternity()))
+                      .virtualColumns(
+                          expressionVirtualColumn(
+                              "v0",
+                              "null",
+                              ColumnType.ofArray(ColumnType.NESTED_DATA)
+                          )
+                      )
+                      .filters(isNull("arrayObject"))
+                      .columns("v0")
+                      .limit(1)
+                      .context(QUERY_CONTEXT_DEFAULT)
+                      .legacy(false)
+                      .resultFormat(ScanQuery.ResultFormat.RESULT_FORMAT_COMPACTED_LIST)
+                      .build()
+            )
+        )
+        .expectedResults(
+            NullHandling.replaceWithDefault() ?
+            ImmutableList.of(new Object[]{null}) : ImmutableList.of()
+        )
+        .expectedSignature(
+            RowSignature.builder()
+                        .add("EXPR$0", ColumnType.ofArray(ColumnType.NESTED_DATA))
+                        .build()
+        )
+        .run();
+  }
+
   @Test
   public void testUnnestJsonQueryArrays()
   {