protected function processUnsubscribe(Session $session, UnsubscribeMessage $msg)
    {
        $subscription = false;
        // should probably be more efficient about this - maybe later
        /** @var SubscriptionGroup $subscriptionGroup */
        foreach ($this->subscriptionGroups as $subscriptionGroup) {
            $result = $subscriptionGroup->processUnsubscribe($session, $msg);

            if ($result !== false) {
                $subscription = $result;
            }
        }

        if ($subscription === false) {
            $errorMsg = ErrorMessage::createErrorMessageFromMessage($msg);
            $session->sendMessage($errorMsg->setErrorURI('wamp.error.no_such_subscription'));

            return;
        }
    }