public ObjectProperty<Node> graphicProperty() {
        if (null == graphic) {
            graphic = new ObjectPropertyBase<>() {
                @Override protected void invalidated() {
                	fireTileEvent(GRAPHIC_EVENT);
                	fireTileEvent(RESIZE_EVENT);
                }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "graphic"; }
            };
        }
        return graphic;
    }
Defines an optional node that can be used in combination with the
CustomTileSkin.
@param GRAPHIC
src/main/java/eu/hansolo/tilesfx/Tile.java