@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

    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

  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) {