fix crash

tournaments/signals.py

@@ -62,7 +62,7 @@ def send_discord_message(webhook_url, content):
 def unregister_team(sender, instance, **kwargs):
     team_registration = instance
     tournament = instance.tournament
-    if tournament.is_deleted is True:
+    if not tournament or tournament.is_deleted is True:
         return
 
     # Create unregistered player records and track captain/other player