static ItIt<S> tlftifyLineIterator(Iterator<S> it) {
  ret it == null ? null : iff_endOnNull(func -> S {
    while (it.hasNext()) {
      S line = it.next();
      if (nempty(line = trim(line))) ret line;
    }
    null;
  });
}

Began life as a copy of #1022556