StackedBarChart does not display negative values

[schaarsc]

the internal logic expects styleClass "negative" to be set, but as soon as a series is added the styleClass is reset to defaults.

public void testBarChart(Stage stage) throws Exception {
    CategoryAxis xAxis = new CategoryAxis();
    NumberAxis yAxis = new NumberAxis();

    // not ok
    StackedBarChart<String, Number> barChart1 = new StackedBarChart<String, Number>(xAxis, yAxis);
    XYChart.Series<String, Number> series1 = new XYChart.Series<String, Number>();
    series1.setName("Serie1");
    series1.getData().add(new XYChart.Data<String, Number>("negative", -10.1));
    barChart1.getData().add(series1);

    // ok
    StackedBarChart<String, Number> barChart2 = new StackedBarChart<String, Number>(xAxis, yAxis){
      @Override protected void seriesChanged(ListChangeListener.Change<? extends Series> c) {}      
    };
    XYChart.Series<String, Number> series2 = new XYChart.Series<String, Number>();
    series2.setName("Serie2");
    series2.getData().add(new XYChart.Data<String, Number>("negative", -20.2));
    barChart2.getData().add(series2);
   
    VBox vbox = new VBox(barChart1, barChart2);
    Scene scene = new Scene(vbox, 500, 500);
    stage.setScene(scene);
    stage.show();
}