return receiver; } else {  return null;
    public MuwsEventReceiver lookup(String key) {        if(key == null || key.length() == 0) {            return null;        }        WeakReference<MuwsEventReceiver> ref = entries.get(key);        if (ref != null) {            MuwsEventReceiver receiver = ref.get();            if(receiver==null) {                //obsolete match                synchronized(this) {                    entries.remove(key);                }            }            return receiver;        } else {            //no match            return null;        }    }