protected function registerSessionHandler()
    {
        if ($this->handler !== null) {
            if (!is_object($this->handler)) {
                if (is_string($this->handler) && Reaction::$app->has($this->handler)) {
                    $this->handler = Reaction::$app->get($this->handler);
                } else {
                    $this->handler = Reaction::create($this->handler);
                }
            }
            if (!$this->handler instanceof SessionHandlerInterface) {
                throw new InvalidConfigException('"' . get_class($this) . '::handler" must implement the \Reaction\Web\Sessions\SessionHandlerInterface.');
            }
        } else {
            throw new InvalidConfigException('"' . get_class($this) . '::handler" can not be empty.');
        }
    }