}
  }

  /**
   * 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