@Override
 public Optional<PersistentUser> findByCredentials(final Credentials credentials) {
   final String identifier = credentials.getIdentifier();
   if (isBlank(identifier)) {
     return Optional.empty();
   }
   return _userRepository.findByEmailIgnoreCase(identifier);
 }
 @Override
 public Optional<PersistentUser> findByUuid(final UUID userId) {
   return _userRepository.findByUserId(userId);
 }