fix(Calendar): null attachment

src/Monitor/Framework/Controller/CalendarController.php

@@ -29,10 +29,13 @@ class CalendarController extends AbstractController
 
         $monitors = $monitorRepository->whereAirDateNotNull();
         $calendar->event(Map::from($monitors)->map(function (Monitor $monitor) {
-            return new Event($monitor->getTitle())
+            $event = new Event($monitor->getTitle())
                 ->startsAt($monitor->getAirDate())
-                ->attachment($monitor->getPoster())
                 ->fullDay();
+            if (null !== $monitor->getPoster()) {
+                $event->attachment($monitor->getPoster());
+            }
+            return $event;
         })->toArray());
 
         return new Response($calendar->get(), 200, [