Http\Client\Promise\HttpFulfilledPromise::then PHP Method

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