* than all other values, and orders the rest using {@code valueComparator} on the contained
   * value.
   *
   * @since 22.0 (but only since 33.4.0 in the Android flavor)
   */
  public static <T> Comparator<Optional<T>> emptiesFirst(Comparator<? super T> valueComparator) {
    checkNotNull(valueComparator);
    return Comparator.<Optional<T>, @Nullable T>comparing(

  }

  TreeMultimap(Comparator<? super K> keyComparator, Comparator<? super V> valueComparator) {
    super(new TreeMap<K, Collection<V>>(keyComparator));
    this.keyComparator = keyComparator;
    this.valueComparator = valueComparator;
  }

  private TreeMultimap(
      Comparator<? super K> keyComparator,
      Comparator<? super V> valueComparator,
      Multimap<? extends K, ? extends V> multimap) {

    assertThat(copy.keySet()).containsExactly(null, "tree", "google").inOrder();
    assertEquals(multimap.keyComparator(), copy.keyComparator());
    assertEquals(multimap.valueComparator(), copy.valueComparator());
  }

     * @since 19.0
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
      super.orderEntriesByValue(valueComparator);
      return this;
    }

    @Override
    @CanIgnoreReturnValue
    Builder<K, V> combine(ImmutableMap.Builder<K, V> builder) {
      super.combine(builder);

     *
     * @since 8.0
     */
    @CanIgnoreReturnValue
    public Builder<K, V> orderValuesBy(Comparator<? super V> valueComparator) {
      this.valueComparator = checkNotNull(valueComparator);
      return this;
    }

    @CanIgnoreReturnValue
    Builder<K, V> combine(Builder<K, V> other) {
      if (other.builderMap != null) {

      super.putAll(entries);
      return this;
    }

    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
      super.orderEntriesByValue(valueComparator);
      return this;
    }

    @CanIgnoreReturnValue
    Builder<K, V> combine(Builder<K, V> other) {
      super.combine(other);
      return this;
    }

     * @since 19.0
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
      super.orderEntriesByValue(valueComparator);
      return this;
    }

    @Override
    @CanIgnoreReturnValue
    Builder<K, V> combine(ImmutableMap.Builder<K, V> builder) {
      super.combine(builder);

     *
     * @since 8.0
     */
    @CanIgnoreReturnValue
    public Builder<K, V> orderValuesBy(Comparator<? super V> valueComparator) {
      this.valueComparator = checkNotNull(valueComparator);
      return this;
    }

    @CanIgnoreReturnValue
    Builder<K, V> combine(Builder<K, V> other) {
      if (other.builderMap != null) {

    SortedSetMultimap<String, Integer> multimap = synchronizedSortedSetMultimap(delegate);
    checkUnmodifiableMultimap(multimap, false, "null", 42);
    assertSame(INT_COMPARATOR, multimap.valueComparator());
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testSerializingUnmodifiableSynchronizedTreeMultimap() {
    TreeMultimap<String, Integer> delegate =

    transient Supplier<? extends SortedSet<V>> factory;
    transient @Nullable Comparator<? super V> valueComparator;

    CustomSortedSetMultimap(Map<K, Collection<V>> map, Supplier<? extends SortedSet<V>> factory) {
      super(map);
      this.factory = checkNotNull(factory);
      valueComparator = factory.get().comparator();
    }

    @Override
    Set<K> createKeySet() {