static S hselect_allowEmpty(Map map, O... params) {
  new StringBuilder buf;
  buf.append("<option></option>\n");
  if (nempty(map)) for (O key : keys(map)) {
    O value = map.get(key);
    buf.append(tag("option", htmlencode(str(or(value, ""))), value := str(key))).append("\n");
  }
  ret tag("select", buf, params) + "\n";
}