gistfile1.php

    protected function setResponse($code, $response = null, $headers = null) {
        if (!is_array($response)) {
            throw new InvalidArgumentException('Second argument only accepts arrays.');
        }

        $keys = array_keys($response);
        $this->_keys = array_merge($this->_keys, $keys);
        $this->set($response);
        $this->set('_serialize', $this->_keys);

        $this->response->statusCode($code);
        if (is_array($headers)) {
            $this->response->header($this->flatten($headers));
        }
    }