}

  private static final Comparator<?> NATURAL_ORDER = Ordering.natural();

  // TODO(b/345814817): Move this to RegularImmutableSortedSet?
  @SuppressWarnings({"unchecked", "ClassInitializationDeadlock"})
  private static final ImmutableSortedSet<Object> NATURAL_EMPTY_SET =
      new RegularImmutableSortedSet<Object>(
          new TreeSet<Object>((Comparator<Object>) NATURAL_ORDER), false);

    }
  }

  /** A singleton implementation of iterator() for the empty ImmutableList. */
  // TODO(b/345814817): Move this to RegularImmutableList?
  @SuppressWarnings("ClassInitializationDeadlock")
  private static final UnmodifiableListIterator<Object> EMPTY_ITR =
      new Itr<Object>(RegularImmutableList.EMPTY, 0);

  private static final class Itr<E> extends AbstractIndexedListIterator<E> {