public function jsonSerialize()
    {
        return array_filter(
            [
                'click_tracking' => $this->getClickTracking(),
                'open_tracking' => $this->getOpenTracking(),
                'subscription_tracking' => $this->getSubscriptionTracking(),
                'ganalytics' => $this->getGanalytics()
            ],
            function ($value) {
                return $value !== null;
            }
        ) ?: null;
    }