public static function init($key = null)
    {
        $instance = Injector::inst()->get(__CLASS__);

        if (empty($key)) {
            user_error(
                'HybridSession::init() was not given a $key. Disabling cookie-based storage',
                E_USER_WARNING
            );
        } else {
            $instance->setKey($key);
        }

        session_set_save_handler($instance, true);

        self::$enabled = true;
    }