public ObservableList<ChartData> getChartData() {
        if (null == chartDataList) { chartDataList = FXCollections.observableArrayList(); }
        return chartDataList;
    }
Defines an optional node that can be used in combination with the
CustomTileSkin.
@param GRAPHIC
src/main/java/eu/hansolo/tilesfx/Tile.java