DATAJPA-1418 - Polishing.

Added comment with issue id on the test.
Added a comment with a link to the Hibernate issue.

Original pull request: #294.

Author: schauder

src/main/java/org/springframework/data/jpa/repository/query/QueryUtils.java

@@ -633,6 +633,9 @@ private static boolean requiresJoin(@Nullable Bindable<?> propertyPathModel, boo
 			return false;
 		}
 
+		// if this path is part of the select list we need to generate an explicit outer join in order to prevent Hibernate
+		// to use an inner join instead.
+		// see https://hibernate.atlassian.net/browse/HHH-12999.
 		if (isLeafProperty && !isForSelection && !attribute.isCollection()) {
 			return false;
 		}

src/test/java/org/springframework/data/jpa/repository/projections/ProjectionJoinIntegrationTests.java

@@ -47,7 +47,7 @@ public class ProjectionJoinIntegrationTests {
 
 	@Autowired private UserRepository userRepository;
 
-	@Test
+	@Test // DATAJPA-1418
 	public void findByIdPerformsAnOuterJoin() {
 		User user = userRepository.save(new User());