testComparator(comparator, empty, z, abc);

    // Just demonstrate that no explicit type parameter is required
    Comparator<Optional<String>> unused = emptiesFirst(naturalOrder());
  }

  public void testEmptiesLast() {
    Optional<String> empty = Optional.empty();
    Optional<String> abc = Optional.of("abc");
    Optional<String> z = Optional.of("z");