return (Collector) TO_IMMUTABLE_LIST;
  }

  // Sets

  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E> Collector<E, ?, ImmutableSet<E>> toImmutableSet() {
    return (Collector) TO_IMMUTABLE_SET;
  }

  static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(
      Comparator<? super E> comparator) {
    checkNotNull(comparator);

   *
   * <p><b>{@code Stream} equivalent:</b> {@code ImmutableSet.copyOf(stream.iterator())}, or pass
   * {@link ImmutableSet#toImmutableSet} to {@code stream.collect()}.
   *
   * @throws NullPointerException if any element is {@code null}
   * @since 14.0 (since 12.0 as {@code toImmutableSet()}).
   */
  @SuppressWarnings("nullness") // Unsafe, but we can't do much about it now.
  public final ImmutableSet<@NonNull E> toSet() {

   * {@link ImmutableSet#toImmutableSet} from consumers of {@code ImmutableSortedSet}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link ImmutableSortedSet#toImmutableSortedSet}.
   * @since 21.0
   */
  @DoNotCall("Use toImmutableSortedSet")
  @Deprecated
  public static <E> Collector<E, ?, ImmutableSet<E>> toImmutableSet() {
    throw new UnsupportedOperationException();

    return new SerializedForm<E>(comparator, toArray());
  }

  /**
   * Not supported. Use {@link #toImmutableSortedSet} instead. This method exists only to hide
   * {@link ImmutableSet#toImmutableSet} from consumers of {@code ImmutableSortedSet}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link ImmutableSortedSet#toImmutableSortedSet}.