.addEqualityGroup(Predicates.isNull())
        .testEquals();
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testNotNull_serialization() {
    checkSerialization(Predicates.notNull());
  }

  public void testIn_apply() {
    Collection<Integer> nums = Arrays.asList(1, 5);
    Predicate<@Nullable Integer> isOneOrFive = Predicates.in(nums);