@Override
  public @NotNull Collection<V> values() {
    Collection<V> result = new ArrayList<>();
    Collection<ValueReference<K, V>> refs = myMap.values();
    for (ValueReference<K, V> ref : refs) {
      V value = ref.get();
      if (value != null) {
        result.add(value);
      }
    }
    return result;
  }
@Override
  public @NotNull Collection<V> values()