Http\Client\Promise\HttpRejectedPromise::then PHP 메소드

    public function then(callable $onFulfilled = null, callable $onRejected = null)
    {
        if (null === $onRejected) {
            return $this;
        }
        try {
            return new HttpFulfilledPromise($onRejected($this->exception));
        } catch (Exception $e) {
            return new self($e);
        }
    }