public void shouldSortMailWithNestedStringBasedSortCriteriaNullsFirst() {
MailUser fooMailUser = new MailUser("foo");
em.persist(fooMailUser);
MailMessage message1 = new MailMessage();
message1.setContent("abc");
MailSender sender1 = new MailSender("foo");
sender1.setMailUser(fooMailUser);
message1.setMailSender(sender1);
MailMessage message2 = new MailMessage();
message2.setContent("abc");
mailMessageRepository.save(message1);
mailMessageRepository.save(message2);
Page<MailMessage> page = mailMessageRepository.findAll(new PageRequest(0, 10, new Sort(Sort.Direction.ASC,