Make content of tag an empty object rather than null

synapse/server_notices/resource_limits_server_notices.py

@@ -153,7 +153,7 @@ class ResourceLimitsServerNotices(object):
                 need_to_set_tag = False
         if need_to_set_tag:
             yield self._store.add_tag_to_room(
-                user_id, room_id, SERVER_NOTICE_ROOM_TAG, None
+                user_id, room_id, SERVER_NOTICE_ROOM_TAG, {}
             )
 
     @defer.inlineCallbacks

synapse/server_notices/server_notices_manager.py

@@ -154,7 +154,7 @@ class ServerNoticesManager(object):
         )
         room_id = info['room_id']
         yield self._store.add_tag_to_room(
-            user_id, room_id, SERVER_NOTICE_ROOM_TAG, None
+            user_id, room_id, SERVER_NOTICE_ROOM_TAG, {},
         )
 
         logger.info("Created server notices room %s for %s", room_id, user_id)