public function attachToRoom($id = null, $identifier = null, $username = null, $room_id = null, $code = null)
    {
        $fields = [];

        if (!is_null($id)) $fields['id'] = $id;
        if (!is_null($identifier)) $fields['identifier'] = $identifier;
        if (!is_null($username)) $fields['username'] = $username;
        if (!is_null($room_id)) $fields['room_id'] = $room_id;
        if (!is_null($code)) $fields['code'] = $code;

        return $this->_post($fields, 'room');
    }