}

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

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

    @Override
    public K getKey() {
      return key;