static <A extends Concept> A ccopyFields(Concept x, A y, S... fields) {
  if (x == null || y == null) ret y;
  if (empty(fields)) { // assume we should copy all fields
    for (S field : conceptFields(x))
      cset(y, field, cget(x, field));
  } else 
    for (S field : fields) {
      O o = cget(x, field);
      if (o != null)
        cset(y, field, o);
    }
  ret y;
}

Began life as a copy of #1002178