DATAMONGO-2293 - Fix EntityOperations id population nulling out entire entity.

We now no longer null the entire entity if a given id value is actually null.

Original Pull Request: #742

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/EntityOperations.java

@@ -48,6 +48,7 @@ import com.mongodb.util.JSONParseException;
  *
  * @author Oliver Gierke
  * @author Mark Paluch
+ * @author Christoph Strobl
  * @since 2.1
  * @see MongoTemplate
  * @see ReactiveMongoTemplate
@@ -614,22 +615,19 @@ class EntityOperations {
 		public T populateIdIfNecessary(@Nullable Object id) {
 
 			if (id == null) {
-				return null;
+				return propertyAccessor.getBean();
 			}
 
-			T bean = propertyAccessor.getBean();
 			MongoPersistentProperty idProperty = entity.getIdProperty();
-
 			if (idProperty == null) {
-				return bean;
+				return propertyAccessor.getBean();
 			}
 
 			if (identifierAccessor.getIdentifier() != null) {
-				return bean;
+				return propertyAccessor.getBean();
 			}
 
 			propertyAccessor.setProperty(idProperty, id);
-
 			return propertyAccessor.getBean();
 		}
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/EntityOperationUnitTests.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.support.DefaultConversionService;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.mongodb.core.EntityOperations.AdaptibleEntity;
+import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
+
+/**
+ * @author Christoph Strobl
+ */
+public class EntityOperationUnitTests {
+
+	EntityOperations ops;
+	MongoMappingContext mappingContext = new MongoMappingContext();
+	ConversionService conversionService = new DefaultConversionService();
+
+	@Before
+	public void setUp() {
+		ops = new EntityOperations(mappingContext);
+	}
+
+	@Test // DATAMONGO-2293
+	public void populateIdShouldReturnTargetBeanWhenIdIsNull() {
+		assertThat(initAdaptibleEntity(new DomainTypeWithIdProperty()).populateIdIfNecessary(null)).isNotNull();
+	}
+
+	<T> AdaptibleEntity<T> initAdaptibleEntity(T source) {
+		return ops.forEntity(source, conversionService);
+	}
+
+	private static class DomainTypeWithIdProperty {
+
+		@Id String id;
+		String value;
+	}
+}