message: do more explicit check
diff: @@ -183,7 +183,7 @@ class TagOrderStore extends Store {
  const rooms =
  GroupStore.getGroupRooms(groupId)
  .map(r => client.getRoom(r.roomId)) // to Room objects
  - .filter(r => !!r); // filter out rooms we haven't joined from the group
  + .filter(r => r !== null && r !== undefined); // filter out rooms we haven't joined from the group
  const badge = rooms && RoomNotifs.aggregateNotificationCount(rooms);
  changedBadges[groupId] = (badge && badge.count !== 0) ? badge : undefined;
  });
  