*/
  private static <K extends @Nullable Object, V extends @Nullable Object>
      Collection<Entry<K, V>> unmodifiableEntries(Collection<Entry<K, V>> entries) {
    if (entries instanceof Set) {
      return Maps.unmodifiableEntrySet((Set<Entry<K, V>>) entries);
    }
    return new Maps.UnmodifiableEntries<>(Collections.unmodifiableCollection(entries));
  }

  /**