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

    return ((Comparable<Object>) left).compareTo(right);
  }

  @Override
  public <S extends Comparable<?>> Ordering<@Nullable S> nullsFirst() {
    Ordering<@Nullable Comparable<?>> result = nullsFirst;
    if (result == null) {
      result = nullsFirst = super.<Comparable<?>>nullsFirst();
    }
    return (Ordering<@Nullable S>) result;
  }

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

    // ordering.reverse() might be optimized, so let it do its thing
    return ordering.<T>reverse().<@NonNull S>nullsFirst();
  }

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

  @SuppressWarnings("unchecked") // still need the right way to explain this
  @Override

                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    SafeTreeSet<String> set = new SafeTreeSet<>(Ordering.natural().nullsFirst());
                    Collections.addAll(set, elements);
                    return new StandardImplForwardingNavigableSet<>(set);
                  }

                  @Override

                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    SafeTreeSet<String> set = new SafeTreeSet<>(Ordering.natural().nullsFirst());
                    Collections.addAll(set, elements);
                    return new StandardImplForwardingNavigableSet<>(set);
                  }

                  @Override

  }

  private TreeMultimap<String, Integer> createMultimap() {
    TreeMultimap<String, Integer> multimap =
        TreeMultimap.create(
            Ordering.<String>natural().nullsFirst(), Ordering.<Integer>natural().nullsFirst());
    multimap.put("a", -1);
    multimap.put("a", -3);
    multimap.put("z", -2);
    return multimap;
  }

  @Override
  protected Map<String, Collection<Integer>> makeEmptyMap() {

  }

  private TreeMultimap<String, Integer> createMultimap() {
    TreeMultimap<String, Integer> multimap =
        TreeMultimap.create(
            Ordering.<String>natural().nullsFirst(), Ordering.<Integer>natural().nullsFirst());
    multimap.put("a", -1);
    multimap.put("a", -3);
    multimap.put("z", -2);
    return multimap;
  }

  @Override
  protected Map<String, Collection<Integer>> makeEmptyMap() {

  }

  @Override
  protected SortedMap<String, Integer> makeEmptyMap() {
    return new SimpleForwardingSortedMap<>(
        new TreeMap<String, Integer>(Ordering.<String>natural().nullsFirst()));
  }

  @Override
  protected SortedMap<String, Integer> makePopulatedMap() {
    final SortedMap<String, Integer> sortedMap = makeEmptyMap();
    sortedMap.put("one", 1);
    sortedMap.put("two", 2);

  }

  @Override
  protected SortedMap<String, Integer> makeEmptyMap() {
    return new SimpleForwardingSortedMap<>(
        new TreeMap<String, Integer>(Ordering.<String>natural().nullsFirst()));
  }

  @Override
  protected SortedMap<String, Integer> makePopulatedMap() {
    final SortedMap<String, Integer> sortedMap = makeEmptyMap();
    sortedMap.put("one", 1);
    sortedMap.put("two", 2);

                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    NavigableSet<String> set = new SafeTreeSet<>(Ordering.natural().nullsFirst());
                    Collections.addAll(set, elements);
                    return set;
                  }

                  @Override
                  public List<String> order(List<String> insertionOrder) {