docs: private ConciseSet convert(IntSet c)
    {
      if (c instanceof ConciseSet && simulateWAH == ((ConciseSet) c).simulateWAH) {
        return (ConciseSet) c;
      }
      if (c == null) {
        return empty();
      }
  
      ConciseSet res = empty();
      IntIterator itr = c.iterator();
      while (itr.hasNext()) {
        res.add(itr.next());
      }
      return res;
    }