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

      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

    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);

    checkNotNull(valueComparator);
    return Comparator.<Optional<T>, @Nullable T>comparing(
        o -> orElseNull(o), Comparator.nullsFirst(valueComparator));
  }

  /**
   * Returns a comparator of {@link Optional} values which treats {@link Optional#empty} as greater

    return insertionOrder;
  }

  /**
   * Compares strings in natural order except that null comes immediately before a given value. This
   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */

  }

  public void testEncloseAll_nullValue() {
    List<@Nullable Integer> nullFirst = Lists.newArrayList(null, 0);
    assertThrows(NullPointerException.class, () -> Range.encloseAll((List<Integer>) nullFirst));
    List<@Nullable Integer> nullNotFirst = Lists.newArrayList(0, null);

  }

  public void testEncloseAll_nullValue() {
    List<@Nullable Integer> nullFirst = Lists.newArrayList(null, 0);
    assertThrows(NullPointerException.class, () -> Range.encloseAll((List<Integer>) nullFirst));
    List<@Nullable Integer> nullNotFirst = Lists.newArrayList(0, null);