(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

   * ImmutableMap#toImmutableMap(Function, Function)} from consumers of {@code ImmutableBiMap}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link ImmutableBiMap#toImmutableBiMap}.
   */
  @Deprecated
  @DoNotCall("Use toImmutableBiMap")
  public static <T extends @Nullable Object, K, V>
      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(

        toImmutableMap(Entry::getKey, Entry::getValue);
    assertThrows(
        IllegalArgumentException.class,
        () -> Stream.of(mapEntry("one", 1), mapEntry("one", 11)).collect(collector));
  }

  public void testToImmutableMapMerging() {
    Collector<Entry<String, Integer>, ?, ImmutableMap<String, Integer>> collector =
        toImmutableMap(Entry::getKey, Entry::getValue, Integer::sum);

  public 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) {
    return CollectCollectors.toImmutableMap(keyFunction, valueFunction);
  }

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableMap} whose keys

   *
   * @since 21.0
   */
  public 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) {
    return CollectCollectors.toImmutableMap(keyFunction, valueFunction);
  }

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableMap} whose keys

   * ImmutableSortedMap}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link ImmutableSortedMap#toImmutableSortedMap}.
   */
  @DoNotCall("Use toImmutableSortedMap")
  @Deprecated
  public static <T extends @Nullable Object, K, V>
      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(

  private static final long serialVersionUID = 0;

  /**
   * Not supported. Use {@link #toImmutableSortedMap}, which offers better type-safety, instead.
   * This method exists only to hide {@link ImmutableMap#toImmutableMap} from consumers of {@code
   * ImmutableSortedMap}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link ImmutableSortedMap#toImmutableSortedMap}.

   * which result will be mapped to that key in the returned map.
   *
   * <p><b>{@code Stream} equivalent:</b> use {@code stream.collect(ImmutableMap.toImmutableMap(k ->
   * k, valueFunction))}. {@code ImmutableMap.copyOf(stream.collect(Collectors.toMap(k -> k,
   * valueFunction)))} behaves similarly, but may not preserve the order of entries.
   *

   *
   * <pre>{@code
   * import static com.google.common.collect.ImmutableMap.toImmutableMap;
   * ...
   * ImmutableMap<Color, String> colorNames =
   *     allColors.stream().collect(toImmutableMap(c -> c, c -> c.toString()));
   * }</pre>
   *
   * <p>Streams provide a more standard and flexible API and the lambdas make it clear what the keys