src/Http/Client/Guzzle/RequestBuilder.php
protected function executeCallableChain()
    {
        $callableResult = null;
        foreach ($this->callableChain as $callable) {
            $callableResult = call_user_func($callable);

            if (null !== $callableResult) {
                break;
            }
        }

        return $callableResult;
    }
protected function executeCallableChain()
    {
        $callableResult = null;
        foreach ($this->callableChain as $callable) {
            $callableResult = call_user_func($callable);

            if (null !== $callableResult) {
                break;
            }
        }

        return $callableResult;
    }
Execute callable chain and return callable result.

@return mixed