@Override
    public Optional<String> validate(String password) {
        return Strings.isNullOrEmpty(password)
                ? Optional.of(EMPTY_PASSWORD_REASONING)
                : Optional.empty();
    }
@Test
    public void testValidateFailure() {
        Optional<String> result = emptyStringValidator.validate("");
        Assert.assertTrue(result.isPresent());
        Assert.assertEquals(result.get(), "must not be empty");
    }