public final ImmutableList<V> replaceValues(K key, Iterable<? extends V> values) {
    throw new UnsupportedOperationException();
  }

  /**
   * @serialData number of distinct keys, and then for each distinct key: the key, the number of
   *     values for that key, and the key's values
   */
  @GwtIncompatible // java.io.ObjectOutputStream
  @J2ktIncompatible