DATAREST-1249 - DomainObjectMerger now properly binds to uninitialized target collections.

Author: odrotbohm

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/DomainObjectReader.java

@@ -480,7 +480,9 @@ private Optional<Collection<Object>> mergeCollections(PersistentProperty<?> prop
 	@SuppressWarnings("unchecked")
 	private static Collection<Object> asCollection(Object source) {
 
-		if (source instanceof Collection) {
+		if (source == null) {
+			return null;
+		} else if (source instanceof Collection) {
 			return (Collection<Object>) source;
 		} else if (source.getClass().isArray()) {
 			return Arrays.asList(ObjectUtils.toObjectArray(source));

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/DomainObjectReaderUnitTests.java

@@ -112,6 +112,7 @@ public void setUp() {
 		mappingContext.getPersistentEntity(CollectionOfEnumWithMethods.class);
 		mappingContext.getPersistentEntity(SampleWithReference.class);
 		mappingContext.getPersistentEntity(Note.class);
+		mappingContext.getPersistentEntity(WithNullCollection.class);
 		mappingContext.afterPropertiesSet();
 
 		this.entities = new PersistentEntities(Collections.singleton(mappingContext));
@@ -555,6 +556,17 @@ public void patchWithReferenceToRelatedEntityIsResolvedCorrectly() throws Except
 		assertThat(result.tags).contains(second);
 	}
 
+	@Test // DATAREST-1249
+	public void mergesIntoUninitializedCollection() throws Exception {
+
+		ObjectMapper mapper = new ObjectMapper();
+		ObjectNode source = (ObjectNode) mapper.readTree("{ \"strings\" : [ \"value\" ] }");
+
+		WithNullCollection result = reader.readPut(source, new WithNullCollection(), mapper);
+
+		assertThat(result.strings).containsExactly("value");
+	}
+
 	@SuppressWarnings("unchecked")
 	private static <T> T as(Object source, Class<T> type) {
 
@@ -766,4 +778,11 @@ public T deserialize(JsonParser p, DeserializationContext ctxt) throws IOExcepti
 					.findFirst().orElse(null);
 		}
 	}
+
+	// DATAREST-1249
+
+	@JsonAutoDetect(fieldVisibility = Visibility.ANY)
+	static class WithNullCollection {
+		List<String> strings;
+	}
 }