}

  public void testToMap_nullValue() {
    assertThrows(NullPointerException.class, () -> fluent(1, 2, 3).toMap(Functions.constant(null)));
  }

  public void testIndex() {
    ImmutableListMultimap<Integer, String> expected =
        ImmutableListMultimap.<Integer, String>builder()
            .putAll(3, "one", "two")
            .put(5, "three")
            .put(4, "four")

    multimap.putAll(Color.RED, asList(2, 7, 1, 8));
    SerializableTester.reserializeAndAssert(multimap);
    assertEquals(INT_COMPARATOR, multimap.valueComparator());
  }

  public void testIndex() {
    final Multimap<String, Object> stringToObject =
        new ImmutableMultimap.Builder<String, Object>()
            .put("1", 1)
            .put("1", 1L)
            .put("1", "1")
            .put("2", 2)