code: private static synchronized void addFieldGetter(FieldGetter fieldGetter, Integer index, boolean addLast) {
  		checkParameter(fieldGetter);
  		
  		LinkedList<FieldGetter> ret = getCurrentFieldGetters();
  		if (index != null) {
  			ret.add(index, fieldGetter);
  		} else {
  			if (addLast) {
  				ret.addLast(fieldGetter);
  			} else {
  				ret.addFirst(fieldGetter);
  			}
  		}
  		getters = ret.toArray(new FieldGetter[ret.size()]);
  	}
docs: 当 Integer index 不为 null 时，boolean addLast 为无效参数