docs: @SuppressWarnings("unchecked")
     private void processQueue() {
        ValueRef<K, V> ref = (ValueRef<K, V>) queue.poll();
        while (ref != null) {
           // only remove if it is the *exact* same WeakValueRef
           if (ref == map.get(ref.getKey()))
              map.remove(ref.getKey());
  
           ref = (ValueRef<K, V>) queue.poll();
        }
     }