DATAMONGO-1774 - Enforce null constraint checks.

And remove code paths returning null where a reactive wrapper type would be expected.

Original pull request: spring-projects#498.

Author: christophstrobl

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

@@ -898,15 +898,15 @@ <T> Mono<T> findAndModify(Query query, Update update, FindAndModifyOptions optio
 	/**
 	 * Remove the given object from the collection by id.
 	 *
-	 * @param object
+	 * @param object must not be {@literal null}.
 	 * @return
 	 */
 	Mono<DeleteResult> remove(Object object);
 
 	/**
 	 * Removes the given object from the given collection.
 	 *
-	 * @param object
+	 * @param object must not be {@literal null}.
 	 * @param collection must not be {@literal null} or empty.
 	 */
 	Mono<DeleteResult> remove(Object object, String collection);

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

@@ -1455,9 +1455,7 @@ public Mono<DeleteResult> remove(Mono<? extends Object> objectToRemove, String c
 	 */
 	public Mono<DeleteResult> remove(Object object) {
 
-		if (object == null) {
-			return null;
-		}
+		Assert.notNull(object, "Object must not be null!");
 
 		return remove(getIdQueryFor(object), object.getClass());
 	}
@@ -1468,12 +1466,9 @@ public Mono<DeleteResult> remove(Object object) {
 	 */
 	public Mono<DeleteResult> remove(Object object, String collection) {
 
+		Assert.notNull(object, "Object must not be null!");
 		Assert.hasText(collection, "Collection name must not be null or empty!");
 
-		if (object == null) {
-			return null;
-		}
-
 		return doRemove(collection, getIdQueryFor(object), object.getClass());
 	}
 

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

@@ -461,6 +461,11 @@ public void testFindAllAndRemoveFullyReturnsAndRemovesDocuments() {
 		StepVerifier.create(template.findOne(new Query(), Sample.class)).expectNext(data).verifyComplete();
 	}
 
+	@Test(expected = IllegalArgumentException.class) // DATAMONGO-1774
+	public void removeWithNullShouldThrowError() {
+		template.remove((Object)null).subscribe();
+	}
+
 	@Test // DATAMONGO-1774
 	public void removeWithEmptyMonoShouldDoNothing() {