@Test
    public void test_isValid_nullValue() {
        final ConstraintValidatorContext context = null;
        assertTrue(validator.isValid(null, context));
    }

    @Test
    public void test_isValid_blankValue() {
        final ConstraintValidatorContext context = null;
        assertTrue(validator.isValid(" ", context));
        assertTrue(validator.isValid("   ", context));