Stream<String> streamB = Stream.of("b").onClose(closeCountB::incrementAndGet);
    Stream<String> concatenated =
        Stream.<Stream<String>>of(Stream.of("a"), streamB, Stream.empty(), Stream.of("c", "d"))
            .reduce(Stream.empty(), Stream::concat);
    assertThat(concatenated).containsExactly("a", "b", "c", "d").inOrder();
    concatenated.close();
    assertThat(closeCountB.get()).isEqualTo(1);
  }

   *
   * <p><b>Java 8+ users:</b> If passing a single element {@code e}, the {@code Stream} equivalent
   * of this method is {@code Stream.generate(() -> e)}. Otherwise, put the elements in a collection
   * and use {@code Stream.generate(() -> collection).flatMap(Collection::stream)}.
   */
  @SafeVarargs
  public static <T extends @Nullable Object> Iterable<T> cycle(T... elements) {

   */
  @GwtIncompatible // java.io.ObjectOutputStream
  @J2ktIncompatible
  private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    stream.writeObject(valueComparator());
    Serialization.writeMultimap(this, stream);
  }

  @CheckForNull
  Comparator<? super V> valueComparator() {
    return emptySet instanceof ImmutableSortedSet

  @J2ktIncompatible
  private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    stream.writeInt(keySet().size());
    for (K key : keySet()) {
      stream.writeObject(key);
    }
    stream.writeInt(size());
    for (Entry<K, V> entry : entries()) {
      stream.writeObject(entry.getKey());
      stream.writeObject(entry.getValue());
    }
  }

   * Predicates.instanceOf(ArrayList.class)}, which is inconsistent with equals. (See {@link
   * Iterables#filter(Iterable, Class)} for related functionality.)
   *
   * <p><b>{@code Stream} equivalent:</b> {@link java.util.stream.Stream#filter Stream.filter}.
   */
  // TODO(kevinb): how can we omit that Iterables link when building gwt
  // javadoc?
  public static <E extends @Nullable Object> Collection<E> filter(

   *
   * <p>For example:
   *
   * <pre>{@code
   * Stream.of("foo", "quux", "banana", "elephant")
   *     .collect(least(2, comparingInt(String::length)))
   * // returns {"foo", "quux"}
   * }</pre>
   *
   * <p>This {@code Collector} uses O(k) memory and takes expected time O(n) (worst-case O(n log
   * k)), as opposed to e.g. {@code Stream.sorted(comparator).limit(k)}, which currently takes O(n

  }

  public void testToOptionalSingleton() {
    assertThat(Stream.of(1).collect(MoreCollectors.toOptional())).hasValue(1);
  }

  public void testToOptionalNull() {
    Stream<@Nullable Object> stream = Stream.of((Object) null);
    try {
      stream.collect(MoreCollectors.toOptional());
      fail("Expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  /**
   * Copies all bytes from the input stream to the output stream. Does not close or flush either
   * stream.
   *
   * <p><b>Java 9 users and later:</b> this method should be treated as deprecated; use the
   * equivalent {@link InputStream#transferTo} method instead.
   *
   * @param from the input stream to read from
   * @param to the output stream to write to
   * @return the number of bytes copied

   * ImmutableSortedSet.copyOf(elements)}; if you want a {@code List} you can use its {@code
   * asList()} view.
   *
   * <p><b>Java 8+ users:</b> If you want to convert a {@link java.util.stream.Stream} to a sorted
   * {@code ImmutableList}, use {@code stream.sorted().collect(toImmutableList())}.
   *
   * @throws NullPointerException if any element in the input is null
   * @since 21.0
   */

  private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    stream.writeObject(elementSet().comparator());
    Serialization.writeMultiset(this, stream);
  }

  @J2ktIncompatible
  @GwtIncompatible // java.io.ObjectInputStream
  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
    stream.defaultReadObject();