protected function isIp($key) : bool
    {
        if (filter_var($this->param[$key], FILTER_VALIDATE_IP) === false) {
            $this->errors[$key.self::ERROR] =
                ucfirst($this->convertToFieldName($key)).' is not valid '.lcfirst(
                    str_replace('is', '', __FUNCTION__)
                );

            return false;
        }

        return true;
    }