* subject to change.
   *
   * @since 2.0
   */
  public ImmutableList<E> asList() {
    return isEmpty() ? ImmutableList.of() : ImmutableList.asImmutableList(toArray());
  }

  /**
   * Returns {@code true} if this immutable collection's implementation contains references to
   * user-created objects that aren't accessible via this collection's methods. This is generally