NullPointer in BarDataProvider

[fother]

change the content of the class for

public class AdvancedChartExample extends LayoutContainer {

	public class Example extends BaseModel {

		public Example(String month, Integer value) {
			setMonth(month);
			setValue(value);
		}

		public String getMonth() {
			return get("month");
		}

		public Integer getValue() {
			return get("value");
		}

		public void setMonth(String month) {
			set("month", month);
		}

		public void setValue(Integer value) {
			set("value", value);
		}

	}

	@Override
	protected void onRender(Element parent, int index) {
		super.onRender(parent, index);

		List<Example> examples = new ArrayList<Example>();
		examples.add(new Example("Jan", 6));
		examples.add(new Example("Fev", null));

		final ListStore<Example> store = new ListStore<Example>();
		store.add(examples);

		// chart
		String url = !Examples.isExplorer() ? "../../" : "";
		url += "gxt/chart/open-flash-chart.swf";
		final Chart chart = new Chart(url);

		ChartModel model = new ChartModel("Title");
		model.setBackgroundColour("#fefefe");
		model.setLegend(new Legend(Position.TOP, true));
		model.setScaleProvider(ScaleProvider.ROUNDED_NEAREST_SCALE_PROVIDER);

		BarChart bar = new BarChart(BarStyle.GLASS);
		bar.setColour("#00aa00");
		BarDataProvider barProvider = new BarDataProvider("value", "month");
		barProvider.bind(store);
		bar.setDataProvider(barProvider);
		model.addChartConfig(bar);

		chart.setChartModel(model);

		LayoutContainer lc = new LayoutContainer();
		RowLayout rl = new RowLayout();
		lc.setLayout(rl);
		lc.setSize(800, 600);

		RowData data;
		data = new RowData(1, 300, new Margins(10));
		ContentPanel cp = new ContentPanel(new FitLayout());
		cp.setHeading("Chart");
		cp.add(chart);
		cp.setCollapsible(true);
		lc.add(cp, data);

		add(lc);

	}
}

stacktrace

java.lang.NullPointerException: null
	at com.extjs.gxt.charts.client.model.BarDataProvider.populateData(BarDataProvider.java:52)
	at com.extjs.gxt.charts.client.Chart.processModel(Chart.java:234)
	at com.extjs.gxt.charts.client.Chart.setChartModel(Chart.java:168)

[fother]

according to sven this "issue" its fixed in SVN...