*/
  static <K extends @Nullable Object, V extends @Nullable Object> Entry<K, V> unmodifiableEntry(
      final Entry<? extends K, ? extends V> entry) {
    checkNotNull(entry);
    return new AbstractMapEntry<K, V>() {
      @Override
      @ParametricNullness
      public K getKey() {
        return entry.getKey();
      }

      @Override
      @ParametricNullness

    }
  }

  /**
   * Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying
   * map.
   */
  final class WriteThroughEntry extends AbstractMapEntry<K, V> {
    final K key; // non-null
    V value; // non-null

    WriteThroughEntry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    @Override

    }
  }

  /**
   * Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying
   * map.
   */
  final class WriteThroughEntry extends AbstractMapEntry<K, V> {
    final K key; // non-null
    V value; // non-null

    WriteThroughEntry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    @Override