fix crash

tournaments/models/tournament.py

@@ -176,7 +176,10 @@ class Tournament(models.Model):
         return self.end_date is None
 
     def creator(self):
-        return self.event.creator.username
+        if self.event and self.event.creator:
+            return self.event.creator.username
+        else:
+            return None
 
     def private_label(self):
         if self.is_private: