Fix regression in PUT handling for empty nested documents.

The fix for #2174 introduced a bug for our PUT handling of nested documents in case the target object's field value is null as it would only apply the nested value if all Optionals were present. This is, of course not the case.

Fixes #2264.

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

@@ -40,7 +40,6 @@
 import org.springframework.data.rest.webmvc.mapping.Associations;
 import org.springframework.data.rest.webmvc.util.InputStreamHttpInputMessage;
 import org.springframework.data.util.ClassTypeInformation;
-import org.springframework.data.util.Optionals;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.http.converter.HttpMessageNotReadableException;
 import org.springframework.lang.Nullable;
@@ -685,7 +684,10 @@ public void doWithPersistentProperty(PersistentProperty<?> property) {
 			} else if (property.isCollectionLike()) {
 				result = mergeCollections(property, sourceValue, targetValue, mapper);
 			} else if (property.isEntity()) {
-				result = Optionals.mapIfAllPresent(sourceValue, targetValue, (l, r) -> mergeForPut(l, r, mapper));
+
+				result = targetValue.isEmpty()
+						? sourceValue
+						: targetValue.flatMap(t -> sourceValue.map(s -> mergeForPut(s, t, mapper)));
 			} else {
 				result = sourceValue;
 			}

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

@@ -662,6 +662,26 @@ void deserializesCustomCollectionOfPrimitives() throws Exception {
 		assertThat(result.longs).isEqualTo(Arrays.asList(1L, 2L));
 	}
 
+	@Test // GH-2264
+	void nestedEntitiesAreCreatedWhenMissingForPut() throws Exception {
+
+		var outer = new Outer();
+		outer.name = "outer name";
+		outer.prop = "something";
+
+		var node = new ObjectMapper().readTree(
+				"{ \"inner\" : { \"name\" : \"new inner name\", \"readOnly\" : \"readonly value\", \"hidden\" : \"hidden value\" } }");
+
+		var result = reader.readPut((ObjectNode) node, outer, new ObjectMapper());
+
+		assertThat(result).isSameAs(outer);
+		assertThat(result.inner).isNotNull();
+		assertThat(result.inner.prop).isNull();
+		assertThat(result.inner.name).isEqualTo("new inner name");
+		assertThat(result.inner.readOnly).isNull();
+		assertThat(result.inner.hidden).isNull();
+	}
+
 	@SuppressWarnings("unchecked")
 	private static <T> T as(Object source, Class<T> type) {