static <A> A mapToObject(Map<S, O> map, A o) {
  if (map == null) ret o;
  for (S field : keys(map))
    setOpt(o, field, map.get(field));
  ret o;
}

static <A> A mapToObject(Map<S, O> map, Class<A> o) {
  ret mapToObject(map, nu(o));
}