fix mypy : Item "None" of "Optional[datetime]" has no attribute "astimezone"

events/management/commands/create_recurrent_events.py

@@ -62,7 +62,7 @@ class Command(BaseCommand):
                 e.end_inscriptions = e.end_inscriptions.astimezone(localtz).replace(
                     hour=rec_event.end_inscriptions.astimezone(localtz).hour
                 )
-                if e.invitations_start is not None:
+                if e.invitations_start is not None and rec_event.invitations_start is not None:
                     e.invitations_start = e.invitations_start.astimezone(
                         localtz
                     ).replace(hour=rec_event.invitations_start.astimezone(localtz).hour)