static Object shallowClone(Object o) {
  if (o == null)
    return o;
    
  if (o instanceof List)
    ret cloneList((List) o);

  if (o instanceof Map) {
    final Map m = o instanceof TreeMap ? new TreeMap() : new HashMap();
    m.putAll((Map) o);
    return m;
  }
  
  if (o instanceof String || o instanceof Number || o instanceof Boolean)
    return o;
    
  if (o instanceof Object[]) {
    Object[] l = (Object[]) o;
    ret l.clone();
  }
  
  // clone an arbitrary custom object

  //print("Cloning custom: " + o);
  Class c = o.getClass();
  final Object clone = nuEmptyObject(c);
  copyFields(o, clone);
  ret clone;
}