--- a/mod_track_muc_joins/mod_track_muc_joins.lua	Wed Apr 13 11:52:51 2016 +0200
+++ b/mod_track_muc_joins/mod_track_muc_joins.lua	Wed Apr 13 11:53:44 2016 +0200
@@ -33,6 +33,7 @@
 			log("debug", "%s room %s", joined and "Joined" or "Left", room);
 			local rooms = session.rooms_joined;
 			if not rooms then
+				if not joined then return; end
 				session.rooms_joined = { [room] = joined };
 			else
 				rooms[room] = joined;