Fix summons

tournaments/models/team_registration.py

@@ -42,8 +42,8 @@ class TeamRegistration(models.Model):
         matches = [m for m in all_matches if m.end_date is None]
         if matches:
             return matches[0]
-        elif all_matches:
-            return all_matches[0]
+        else:
+            return None
 
     def next_stage(self):
         matches = map(lambda ts: ts.match, self.teamscore_set.all())