code: public List<Option> getSelectedItems() {
          final List<Option> items = new ArrayList<>(0);
          for (Entry<OptionElement, Option> entry : itemMap.entrySet()) {
              Option opt = entry.getValue();
              if (opt.isSelected())
                  items.add(opt);
          }
          return items;
      }
docs: Returns the selected items list. If no item is selected, this method
  returns an empty list.
  
  @return the selected items list