Thruway\Subscription\Subscription::getSubscriptionGroup PHP Method

    public function getSubscriptionGroup()
    {
        return $this->subscriptionGroup;
    }

 /**
  * @param Subscription $subscription
  * @return StateHandlerRegistration|bool|null
  */
 private function getStateHandlerRegistrationForSubscription(Subscription $subscription)
 {
     $subscriptionGroup = $subscription->getSubscriptionGroup();
     if ($subscriptionGroup instanceof SubscriptionGroup) {
         if (!$this->stateHandlerMap->contains($subscriptionGroup)) {
             $this->setupStateHandlerRegistration($subscriptionGroup);
         }
         return $this->stateHandlerMap[$subscriptionGroup];
     }
     Logger::alert($this, "processSubscriptionAdded called with subscription that does not have subscriptionGroup set.");
     return false;
 }