code: public void deselectByIndex(int index) {
          getDispatcher().beforeDeselect(this, index);
          
          new Select(getElement()).deselectByIndex(index);
          if (Config.getBoolConfigProperty(ConfigProperty.ENABLE_GUI_LOGGING)) {
              logUIActions(UIActions.CLEARED, Integer.toString(index));
          }
          
          getDispatcher().afterDeselect(this, index);
      }
docs: Deselect the option at the given index. This is done by examing the "index" attribute of an element, and not
  merely by counting.
  
  @param index
  the index to deselect