    public function setStatusCode($code, $description = null)
    {
        if (isset(self::$status_codes[$code])) {
            $this->statusCode = $code;
        } else {
            throw new InvalidArgumentException("Unrecognised HTTP status code '$code'");
        }

        if ($description) {
            $this->statusDescription = $description;
        } else {
            $this->statusDescription = self::$status_codes[$code];
        }
        return $this;
    }