In Ensemble go to samples->Charts->Pie->Advanced Pie Chart. Click on PieChart Properties and try to uncheck Labels Visible checkbox. You'll get an exception:

java.lang.NullPointerException
at javafx.scene.chart.PieChart.layoutChartChildren(PieChart.java:548)
at javafx.scene.chart.Chart$1.layoutChildren(Chart.java:84)
at javafx.scene.Parent.layout(Parent.java:1018)
at javafx.scene.Scene.layoutDirtyRoots(Scene.java:513)
at javafx.scene.Scene.doLayoutPass(Scene.java:484)
at javafx.scene.Scene.access$3900(Scene.java:169)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2199)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:363)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:460)
at com.sun.javafx.tk.quantum.QuantumToolkit$9.run(QuantumToolkit.java:329)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:76)