@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>())},

  @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<@Nullable S>) result;
  }

  @Override
  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
  public <S extends Comparable<?>> Ordering<S> reverse() {

                .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(

    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

    Ordering<@Nullable Integer> ordering = Ordering.<Integer>natural().<Integer>nullsLast();
    Helpers.<@Nullable Integer>testComparator(ordering, 0, 1, Integer.MAX_VALUE, null);

    new EqualsTester()
        .addEqualityGroup(ordering, Ordering.natural().nullsLast())
        .addEqualityGroup(numberOrdering.nullsLast())
        .addEqualityGroup(Ordering.natural())
        .testEquals();
  }

    Ordering<@Nullable Integer> ordering = Ordering.<Integer>natural().<Integer>nullsLast();
    Helpers.<@Nullable Integer>testComparator(ordering, 0, 1, Integer.MAX_VALUE, null);

    new EqualsTester()
        .addEqualityGroup(ordering, Ordering.natural().nullsLast())
        .addEqualityGroup(numberOrdering.nullsLast())
        .addEqualityGroup(Ordering.natural())
        .testEquals();
  }

   *
   * <p><b>Java 8+ users:</b> Use {@code Comparator.nullsLast(thisComparator)} instead.
   */
  // type parameter <S> lets us avoid the extra <String> in statements like:
  // Ordering<String> o = Ordering.<String>natural().nullsLast();
  @GwtCompatible(serializable = true)
  public <S extends T> Ordering<@Nullable S> nullsLast() {
    return new NullsLastOrdering<S>(this);
  }

  /**

   *
   * <p><b>Java 8+ users:</b> Use {@code Comparator.nullsLast(thisComparator)} instead.
   */
  // type parameter <S> lets us avoid the extra <String> in statements like:
  // Ordering<String> o = Ordering.<String>natural().nullsLast();
  @GwtCompatible(serializable = true)
  public <S extends T> Ordering<@Nullable S> nullsLast() {
    return new NullsLastOrdering<S>(this);
  }

  /**

  };

  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) {