public function error($key = null, $return_error = null, $return_no_error = '')
    {
        if (isset($key)) {
            $result = gplcart_array_get($this->errors, $key);
        } else {
            $result = empty($this->errors) ? null : $this->errors;
        }

        if (isset($result)) {
            return isset($return_error) ? $return_error : $result;
        }

        return $return_no_error;
    }