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