@Override
  @SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
  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

                            .compare(
                                left.getValue(), right.getValue(), Ordering.natural().nullsFirst())
                            .result();
                      }
                    }.sortedCopy(insertionOrder);
                  }
                })
            .named("TreeMultimap nullsFirst")
            .withFeatures(

    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

  }

  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() {

                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) {

      SortedMap<K, V> delegate, Comparator<? super K> comparator) {
    return new ImmutableSortedMap<K, V>(delegate, comparator);
  }

  /*
   * We don't permit nulls, but we wrap every comparator with nullsFirst().
   * Why? We want for queries like containsKey(null) to return false, but the
   * GWT SortedMap implementation that we delegate to throws
   * NullPointerException if the comparator does. Since our construction

 *
 * @author Louis Wasserman
 */
@GwtCompatible
@NullMarked
public class GeneralRangeTest extends TestCase {
  private static final Ordering<@Nullable Integer> ORDERING =
      Ordering.<Integer>natural().<Integer>nullsFirst();

  private static final List<@Nullable Integer> IN_ORDER_VALUES =
      unmodifiableList(Arrays.<@Nullable Integer>asList(null, 1, 2, 3, 4, 5));

  public void testCreateEmptyRangeFails() {

    assertEquals(comparator, elementSet.comparator());
  }

  public void testNullAcceptingComparator() throws Exception {
    Comparator<@Nullable String> comparator = Ordering.<String>natural().<String>nullsFirst();
    TreeMultiset<@Nullable String> ms = TreeMultiset.create(comparator);

    ms.add("b");
    ms.add(null);
    ms.add("a");
    ms.add("b");
    ms.add(null, 2);

  }

  /** Decreasing integer values. A {@code null} comes before any non-null value. */
  private static final Comparator<@Nullable Integer> DECREASING_INT_COMPARATOR =
      Ordering.<Integer>natural().reverse().<Integer>nullsFirst();

  private SetMultimap<String, Integer> create() {
    return TreeMultimap.create(StringLength.COMPARATOR, DECREASING_INT_COMPARATOR);
  }