(ms1, ms2) -> {
          ms1.addAll(ms2);
          return ms1;
        });
  }

  // Maps

  static <T extends @Nullable Object, K, V> Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
      Function<? super T, ? extends K> keyFunction,
      Function<? super T, ? extends V> valueFunction) {
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    return Collector.of(

      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction) {
    throw new UnsupportedOperationException();
  }

  /**
   * Not supported. This method does not make sense for {@code BiMap}. This method exists only to
   * hide {@link ImmutableMap#toImmutableMap(Function, Function, BinaryOperator)} from consumers of

      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction) {
    throw new UnsupportedOperationException();
  }

  /**
   * Not supported. This method does not make sense for {@code BiMap}. This method exists only to
   * hide {@link ImmutableMap#toImmutableMap(Function, Function, BinaryOperator)} from consumers of

   * which result will be mapped to that key in the returned map.
   *
   * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(ImmutableMap.toImmutableMap(k -> k,
   * valueFunction))}.
   *
   * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code
   *     valueFunction} produces {@code null} for any key
   * @since 14.0