public RatingValue increment(Rating rating) {
    if (value.compareTo(rating) > 0) {
      value = rating;
    }
    this.set = true;
    return this;
  }
@Test
  public void increment_has_no_effect_if_arg_is_null() {
    verifyUnsetValue(new RatingValue().increment((RatingValue) null));
  }