code: public MutableIntSet asSet(List<T> list, MutableIntSet setToAppend)
      {
          asSet(list, this, setToAppend);
          return setToAppend;
      }
docs: extracts the int values represented by this attribute from the list and adds them to the setToAppend.
  If the int attribute is null, it's ignored.
  @param list incoming list
  @param setToAppend the set to append to