Polishing.

Reformat code. Refine tests.

See #3849
Original pull request: #3856

Author: mp911de

spring-data-jpa/src/main/java/org/springframework/data/jpa/domain/Specification.java

@@ -57,11 +57,9 @@ static <T> Specification<T> not(@Nullable Specification<T> spec) {
 		return spec == null //
 				? (root, query, builder) -> null //
 				: (root, query, builder) -> {
+
 			Predicate predicate = spec.toPredicate(root, query, builder);
-			if(predicate != null) {
-				return builder.not(predicate);
-			}
-			return builder.disjunction();
+					return predicate != null ? builder.not(predicate) : builder.disjunction();
 		};
 	}
 

spring-data-jpa/src/test/java/org/springframework/data/jpa/domain/SpecificationUnitTests.java

@@ -206,22 +206,21 @@ void orCombinesSpecificationsInOrder() {
 		Predicate secondPredicate = mock(Predicate.class);
 
 		Specification<Object> first = ((root1, query1, criteriaBuilder) -> firstPredicate);
-
 		Specification<Object> second = ((root1, query1, criteriaBuilder) -> secondPredicate);
 
 		first.or(second).toPredicate(root, query, builder);
 
 		verify(builder).or(firstPredicate, secondPredicate);
 	}
 
-	@Test // #3849
+	@Test // GH-3849
 	void notWithNullPredicate() {
-		Specification<Object> spec = (r, q, cb) -> null;
 
-		Specification<Object> notSpec = Specification.not(spec);
+		when(builder.disjunction()).thenReturn(mock(Predicate.class));
+
+		Specification<Object> notSpec = Specification.not((r, q, cb) -> null);
 
-		notSpec.toPredicate(root, query, builder);
-		
+		assertThat(notSpec.toPredicate(root, query, builder)).isNotNull();
 		verify(builder).disjunction();
 	}