code: public void insertItem(T value, String text, int index) {
          insertItemInternal(value, text, index, true);
      }
docs: Inserts an item into the list box, specifying an initial value for the
  item. Has the same effect as
  <pre>insertItem(value, null, item, index)</pre>
  
  @param value the item's value, to be submitted if it is part of a
  {@link FormPanel}.
  @param text  the text of the item to be inserted
  @param index the index at which to insert it