public function has($type = null)
    {
        if ($this->count() <= 0) {
            return false;
        }

        if (is_null($type)) {
            return true;
        }

        if (!$this->typeIsAvailable($type)) {
            return false;
        }

        foreach ($this->notifications as $key => $message) {
            if ($message->getType() == $type) {
                return true;
            }
        }

        return false;
    }