public function append()
    {
        foreach (func_get_args() as $value) {
            if ($value instanceof ResultInterface
                || $value instanceof ApiException
                || is_callable($value)
            ) {
                $this->queue[] = $value;
            } else {
                throw new \InvalidArgumentException('Expected an Api\ResultInterface or Api\Exception\ApiException.');
            }
        }
    }