*/
  @IgnoreJRERequirement // Users will use this only if they're already using streams.
  public static <E extends Enum<E>> Collector<E, ?, ImmutableSet<E>> toImmutableEnumSet() {
    return CollectCollectors.toImmutableEnumSet();
  }

  /**
   * Returns a new, <i>mutable</i> {@code EnumSet} instance containing the given elements in their