Do not throw exception when flat_object field is explicitly null

CHANGELOG.md

@@ -67,6 +67,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fixed array field name omission in flat_object function for nested JSON ([#13620](https://github.com/opensearch-project/OpenSearch/pull/13620))
 - Fix range aggregation optimization ignoring top level queries ([#15194](https://github.com/opensearch-project/OpenSearch/pull/15194))
 - Fix incorrect parameter names in MinHash token filter configuration handling ([#15233](https://github.com/opensearch-project/OpenSearch/pull/15233))
+- Fix indexing error when flat_object field is explicitly null ([#15375](https://github.com/opensearch-project/OpenSearch/pull/15375))
 - Fix split response processor not included in allowlist ([#15393](https://github.com/opensearch-project/OpenSearch/pull/15393))
 - Fix unchecked cast in dynamic action map getter ([#15394](https://github.com/opensearch-project/OpenSearch/pull/15394))
 

rest-api-spec/src/main/resources/rest-api-spec/test/index/100_partial_flat_object.yml

@@ -88,7 +88,16 @@ setup:
             } ]
           }
         }
-
+  - do:
+      index:
+        index: test_partial_flat_object
+        id: 4
+        body: {
+          "issue": {
+            "number": 999,
+            "labels": null
+          }
+        }
   - do:
       indices.refresh:
         index: test_partial_flat_object
@@ -135,7 +144,7 @@ teardown:
           }
         }
 
-  - length: { hits.hits: 3 }
+  - length: { hits.hits: 4 }
 
   # Match Query with exact dot path.
   - do:

server/src/main/java/org/opensearch/index/mapper/FlatObjectFieldMapper.java

@@ -568,11 +568,7 @@ protected void parseCreateField(ParseContext context) throws IOException {
         if (context.externalValueSet()) {
             String value = context.externalValue().toString();
             parseValueAddFields(context, value, fieldType().name());
-        } else if (context.parser().currentToken() == XContentParser.Token.VALUE_NULL) {
-            context.parser().nextToken(); // This triggers an exception in DocumentParser.
-            // We could remove the above nextToken() call to skip the null value, but the existing
-            // behavior (since 2.7) throws the exception.
-        } else {
+        } else if (context.parser().currentToken() != XContentParser.Token.VALUE_NULL) {
             JsonToStringXContentParser jsonToStringParser = new JsonToStringXContentParser(
                 NamedXContentRegistry.EMPTY,
                 DeprecationHandler.IGNORE_DEPRECATIONS,

server/src/test/java/org/opensearch/index/mapper/FlatObjectFieldMapperTests.java

@@ -25,7 +25,6 @@
 
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.core.IsEqual.equalTo;
-import static org.hamcrest.core.StringContains.containsString;
 
 public class FlatObjectFieldMapperTests extends MapperTestCase {
     private static final String FIELD_TYPE = "flat_object";
@@ -133,9 +132,10 @@ public void testDefaults() throws Exception {
 
     public void testNullValue() throws IOException {
         DocumentMapper mapper = createDocumentMapper(fieldMapping(this::minimalMapping));
-        MapperParsingException e = expectThrows(MapperParsingException.class, () -> mapper.parse(source(b -> b.nullField("field"))));
-        assertThat(e.getMessage(), containsString("object mapping for [_doc] tried to parse field [field] as object"));
-
+        ParsedDocument parsedDocument = mapper.parse(source(b -> b.nullField("field")));
+        assertEquals(1, parsedDocument.docs().size());
+        IndexableField[] fields = parsedDocument.rootDoc().getFields("field");
+        assertEquals(0, fields.length);
     }
 
     @Override