event: try to add proper 404 error

src/api/views/events.py

-from rest_framework import generics
-from rest_framework import permissions
+from rest_framework import generics, permissions, status
+from rest_framework.response import Response
+
 
 from core.models.events import Event
 
@@ -24,4 +25,7 @@ class EventDetail(ConferenceSlugMixin, generics.RetrieveUpdateDestroyAPIView):
 
     def get_object(self, **kwargs):
         event_id = self.request.resolver_match.kwargs['pk']
+        try:
             return Event.objects.accessible_by_user(user=self.request.user, conference=self.conference).get(pk=event_id)
+        except Event.DoesNotExist:
+            return Response(status=status.HTTP_404_NOT_FOUND)