code: private void addPaletteItem(String category,IPaletteItem item){
  		if(items.get(category)==null){
  			List<IPaletteItem> list = new ArrayList<IPaletteItem>();
  			items.put(category,list);
  		}
  		List<IPaletteItem> list = items.get(category);
  		list.add(item);
  	}
docs: Adds PaletteItem to the specified category.
  
  @param category the category
  @param item the item