[NFR]When not found option renturn null

[dreamsxin]

        $this->validate(new StringLengthValidator(array(
            'max' => 20,
            'min' => 1,
            'messageMaximum' => 'messageMaximum',
            'messageMinimum' => 'messageMinimum'
        )));

That must be throw error

    PHALCON_INIT_VAR(field);
    phalcon_call_method_p1(field, this_ptr, "getoption", option);
    if (Z_TYPE_P(field) != IS_STRING) {
        PHALCON_THROW_EXCEPTION_STR(phalcon_mvc_model_exception_ce, "Field name must be a string");
        return;
    }

PHP_METHOD(Phalcon_Mvc_Model_Validator, getOption){
    // ```
    RETURN_MM_EMPTY_STRING(); // change to RETURN_MM_NULL()
}