static <A extends Concept> A ccopyFields2(Concept x, A y, Iterable<S> fields) {
  if (x == null || y == null) ret y;
  for (S field : unnull(fields)) {
    O o = cget(x, field);
    if (o != null)
      cset(y, field, o);
  }
  ret y;
}

Began life as a copy of #1013534