java.lang.NullPointerException
        at ensemble.samples.graphics.DigitalClock$Clock.stop(DigitalClock.java:162)
        at ensemble.samples.graphics.DigitalClock.stop(DigitalClock.java:85)
        at ensemble.pages.SamplePage$SamplePageView.stop(SamplePage.java:466)
        at ensemble.Ensemble2.goToPage(Ensemble2.java:337)
        at ensemble.Ensemble2.goToPage(Ensemble2.java:318)
        at ensemble.Ensemble2$6.changed(Ensemble2.java:219)
        at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelp                                                                      er.java:178)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:61)
        at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(ObjectPropertyBase.java:79                                                                      )
        at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:86)
        at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:119)
        at javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:72)
        at javafx.scene.control.MultipleSelectionModelBase$1.invalidated(MultipleSelectionModelBase.                                                                      java:42)
        at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(Expressi                                                                      onHelper.java:137)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:61)
        at javafx.beans.property.IntegerPropertyBase.fireValueChangedEvent(IntegerPropertyBase.java:                                                                      79)
        at javafx.beans.property.IntegerPropertyBase.markInvalid(IntegerPropertyBase.java:86)
        at javafx.beans.property.IntegerPropertyBase.set(IntegerPropertyBase.java:119)
        at javafx.scene.control.SelectionModel.setSelectedIndex(SelectionModel.java:46)
        at javafx.scene.control.MultipleSelectionModelBase.select(MultipleSelectionModelBase.java:23                                                                      4)
        at javafx.scene.control.MultipleSelectionModelBase.clearAndSelect(MultipleSelectionModelBase                                                                      .java:215)
        at com.sun.javafx.scene.control.behavior.TreeCellBehavior.simpleSelect(TreeCellBehavior.java                                                                      :108)
        at com.sun.javafx.scene.control.behavior.TreeCellBehavior.mousePressed(TreeCellBehavior.java                                                                      :72)
        at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:270)
        at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:264)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.ja                                                                      va:56)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:1                                                                      62)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:1                                                                      15)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatc                                                                      her.java:38)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:47)
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
        at javafx.event.Event.fireEvent(Event.java:166)
        at javafx.scene.Scene$MouseHandler.process(Scene.java:2645)
        at javafx.scene.Scene$MouseHandler.process(Scene.java:2466)
        at javafx.scene.Scene$MouseHandler.access$1200(Scene.java:2439)
        at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1209)
        at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:1756)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.ja                                                                      va:185)
        at com.sun.glass.ui.View.handleMouseEvent(View.java:252)
        at com.sun.glass.ui.View.notifyMouse(View.java:512)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
        at com.sun.glass.ui.win.WinApplication$1$1.run(WinApplication.java:49)
        at java.lang.Thread.run(Thread.java:662)