DATAES-845 - MappingElasticsearchConverter handles lists with null values.

Original PR: spring-projects#470

Author: sothawo

src/main/java/org/springframework/data/elasticsearch/core/convert/MappingElasticsearchConverter.java

@@ -595,8 +595,14 @@ private Object writeCollectionValue(Object value, ElasticsearchPersistentPropert
 				: Streamable.of(ObjectUtils.toObjectArray(value));
 
 		List<Object> target = new ArrayList<>();
-		if (!typeHint.getActualType().getType().equals(Object.class) && isSimpleType(typeHint.getActualType().getType())) {
-			collectionSource.map(this::getWriteSimpleValue).forEach(target::add);
+		TypeInformation<?> actualType = typeHint.getActualType();
+		Class<?> type = actualType != null ? actualType.getType() : null;
+
+		if (type != null && !type.equals(Object.class) && isSimpleType(type)) {
+			// noinspection ReturnOfNull
+			collectionSource //
+					.map(element -> element != null ? getWriteSimpleValue(element) : null) //
+					.forEach(target::add);
 		} else {
 
 			collectionSource.map(it -> {
@@ -670,10 +676,6 @@ private boolean requiresTypeHint(TypeInformation<?> type, Class<?> actualType,
 
 	/**
 	 * Compute the type to use by checking the given entity against the store type;
-	 *
-	 * @param entity
-	 * @param source
-	 * @return
 	 */
 	private ElasticsearchPersistentEntity<?> computeClosestEntity(ElasticsearchPersistentEntity<?> entity,
 			Map<String, Object> source) {

src/test/java/org/springframework/data/elasticsearch/core/convert/MappingElasticsearchConverterUnitTests.java

@@ -718,6 +718,23 @@ void shouldNotReadSeqNoPrimaryTermProperty() {
 		assertThat(entity.seqNoPrimaryTerm).isNull();
 	}
 
+	@Test // DATAES-845
+	void shouldWriteCollectionsWithNullValues() throws JSONException {
+		EntityWithListProperty entity = new EntityWithListProperty();
+		entity.setId("42");
+		entity.setValues(Arrays.asList(null, "two", null, "four"));
+
+		String expected = '{' + //
+				"  \"id\": \"42\"," + //
+				"  \"values\": [null, \"two\", null, \"four\"]" + //
+				'}';
+		Document document = Document.create();
+		mappingElasticsearchConverter.write(entity, document);
+		String json = document.toJson();
+
+		assertEquals(expected, json, false);
+	}
+
 	private String pointTemplate(String name, Point point) {
 		return String.format(Locale.ENGLISH, "\"%s\":{\"lat\":%.1f,\"lon\":%.1f}", name, point.getX(), point.getY());
 	}
@@ -932,4 +949,11 @@ static class EntityWithSeqNoPrimaryTerm {
 
 		@Nullable private SeqNoPrimaryTerm seqNoPrimaryTerm;
 	}
+
+	@Data
+	static class EntityWithListProperty {
+		@Id private String id;
+
+		private List<String> values;
+	}
 }