@Override
  public String create(UserDto user) {
    UserDto userDto = requireNonNull(user, "User cannot be null");
    return hash(requireNonNull(emptyToNull(userDto.getEmail()), "Email cannot be null"));
  }
@Test
  public void create_is_case_insensitive() {
    assertThat(underTest.create(UserTesting.newUserDto("john", "John", "john@doo.com"))).isEqualTo(underTest.create(UserTesting.newUserDto("john", "John", "John@Doo.com")));
  }