public void setItemSortingTopic(final ItemSortingTopic ITEM_SORTING_TOPIC) {
        if (null == itemSortingTopic) {
            _itemSortingTopic = ITEM_SORTING_TOPIC;
            fireTileEvent(DATA_EVENT);
        } else {
            if (!itemSortingTopic.isBound()) {
                itemSortingTopic.set(ITEM_SORTING_TOPIC);
            }
        }
    }
Defines an optional node that can be used in combination with the
CustomTileSkin.
@param GRAPHIC
src/main/java/eu/hansolo/tilesfx/Tile.java