Collection<Number> nums = ImmutableSet.of();
    Predicate<Number> p1 = Predicates.in(nums);
    Predicate<Object> p2 = Predicates.<Object>in(nums);
    // The next two lines are not expected to compile.
    // Predicate<Integer> p3 = Predicates.in(nums);
    // Predicate<Integer> p4 = Predicates.<Integer>in(nums);
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester