protected function isAlphaNumeric($key) : bool
    {
        $conCate = ' ';
        $columnName = ucfirst($this->convertToFieldName($key)).' should be ';

        if (isset($this->errors[$key.self::ERROR])) {
            list($conCate, $columnName) = $this->setErrorConcat($key);
        }

        if (!ctype_alnum($this->param[$key])) {
            return $this->setAlphaNumError($key, $conCate, $columnName, 'alpha numeric.');
        }

        return true;
    }