NullPointerException.class,
        () -> {
          ImmutableListMultimap<Object, Integer> unused =
              fluent(1, 2, 3).index(Functions.constant(null));
        });
  }

  public void testIndex_nullValue() {
    assertThrows(
        NullPointerException.class,
        () -> {
          ImmutableListMultimap<String, Integer> unused =
              fluent(1, null, 2).index(Functions.constant("foo"));

          }
        };

    Multimap<Integer, String> index = Multimaps.index(badGuys, stringLengthFunction);

    assertEquals(expectedIndex, index);
  }

  public void testIndex_nullValue() {
    List<@Nullable Integer> values = Arrays.asList(1, null);
    assertThrows(
        NullPointerException.class,
        () -> Multimaps.index((List<Integer>) values, Functions.identity()));
  }