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

  }

  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) {
                    SafeTreeSet<String> set = new SafeTreeSet<>(Ordering.natural().nullsFirst());
                    Collections.addAll(set, elements);
                    return new StandardImplForwardingNavigableSet<>(set);
                  }

                  @Override

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

  /**

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

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

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

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

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

  /**

                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) {

 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
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 = asList(null, 1, 2, 3, 4, 5);

  public void testCreateEmptyRangeFails() {
    for (BoundType lboundType : BoundType.values()) {

  @Override
  protected <K, V> NavigableMap<K, V> create() {
    @SuppressWarnings("unchecked")
    NavigableMap<K, V> innermost =
        new SafeTreeMap<>((Comparator<? super K>) Ordering.natural().nullsFirst());
    TestMap<K, V> inner = new TestMap<>(innermost, mutex);
    NavigableMap<K, V> outer = Synchronized.navigableMap(inner, mutex);
    return outer;
  }