@Override
  @SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
  public <S extends Comparable<?>> Ordering<@Nullable S> nullsLast() {
    Ordering<@Nullable Comparable<?>> result = nullsLast;
    if (result == null) {
      result = nullsLast = super.<Comparable<?>>nullsLast();
    }
    return (Ordering<@Nullable S>) result;
  }

  @Override

  @Parameters
  public static Collection<Object[]> parameters() {
    Comparator<String> nullsLast = Ordering.natural().nullsLast();

    return Arrays.asList(
        new Object[][] {
          {new MapIteratorCache<String, String>(new HashMap<String, String>())},
          {new MapIteratorCache<String, String>(new TreeMap<String, String>(nullsLast))},
          {new MapRetrievalCache<String, String>(new HashMap<String, String>())},

    return ordering.<T>reverse().<@NonNull S>nullsLast();
  }

  @SuppressWarnings("unchecked") // still need the right way to explain this
  @Override
  public <S extends @Nullable T> Ordering<@Nullable S> nullsFirst() {
    return (Ordering<@Nullable S>) this;
  }

  @Override
  public <S extends @Nullable T> Ordering<@Nullable S> nullsLast() {
    return ordering.<@NonNull S>nullsLast();
  }

  @Override

                .compare(a.anInt, b.anInt)
                .compare(a.anEnum, b.anEnum, Ordering.natural().nullsLast())
                .result();
    Comparator<Foo> comparatorUsingComparatorMethods =
        comparing((Foo foo) -> foo.aString)
            .thenComparing(foo -> foo.anInt)
            .thenComparing(foo -> foo.anEnum, nullsLast(naturalOrder()));
    ImmutableList<Foo> instances =
        ImmutableList.of(

 * import static java.util.Comparator.comparing;
 * import static java.util.Comparator.nullsLast;
 * import static java.util.Comparator.naturalOrder;
 *
 * ...
 *   private static final Comparator<Foo> COMPARATOR =
 *       comparing((Foo foo) -> foo.aString)
 *           .thenComparing(foo -> foo.anInt)
 *           .thenComparing(foo -> foo.anEnum, nullsLast(naturalOrder()));
 *
 *   @Override
 *   public int compareTo(Foo that) {

  public static <T> Comparator<Optional<T>> emptiesLast(Comparator<? super T> valueComparator) {
    checkNotNull(valueComparator);
    return Comparator.<Optional<T>, @Nullable T>comparing(
        o -> orElseNull(o), Comparator.nullsLast(valueComparator));
  }

  // For discussion of why this exists, see the Android flavor.
  private static <T> @Nullable T orElseNull(Optional<T> optional) {
    return optional.orElse(null);
  }

  /**

  static final Supplier<TreeSet<String>> STRING_TREESET_FACTORY =
      new Supplier<TreeSet<String>>() {
        @Override
        public TreeSet<String> get() {
          return new TreeSet<>(Ordering.natural().nullsLast());
        }
      };

  static void populateMultimapForGet(Multimap<Integer, String> multimap, String[] elements) {
    multimap.put(2, "foo");
    for (String element : elements) {