Fix accessing undefined variable

public/typo3conf/ext/ep_products/Classes/Service/IcalService.php

@@ -113,7 +113,7 @@ class IcalService implements SingletonInterface
             $occupancy = $event->getOccupancy();
         }
 
-        if (!isset($item['to'])) {
+        if (isset($event) && !isset($item['to'])) {
             $item['to'] = $event->getEnd();
             $this->addOccupancyItem($item);
         }