Caused by: java.lang.NullPointerException
    at javafx.scene.control.TreeView$TreeViewFocusModel$2.handle(TreeView.java:1257)
    at javafx.scene.control.TreeView$TreeViewFocusModel$2.handle(TreeView.java:1231)
    at com.sun.javafx.scene.control.WeakEventHandler.handle(WeakEventHandler.java:62)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:56)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:162)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:115)
    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.EventUtil.fireEventImpl(EventUtil.java:47)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.control.TreeItem.fireEvent(TreeItem.java:748)
    at javafx.scene.control.TreeItem.updateChildren(TreeItem.java:840)
    at javafx.scene.control.TreeItem.access$100(TreeItem.java:197)
    at javafx.scene.control.TreeItem$2.onChanged(TreeItem.java:392)
    at com.sun.javafx.collections.ObservableListWrapper.callObservers(ObservableListWrapper.java:78)
    at com.sun.javafx.collections.ObservableListWrapper.add(ObservableListWrapper.java:97)
    at com.sun.javafx.collections.ObservableListWrapper.add(ObservableListWrapper.java:90)
    at com.javafx.experiments.scenicview.ScenicView$8.onChanged(ScenicView.java:254)
    at com.sun.javafx.collections.ObservableListWrapper.callObservers(ObservableListWrapper.java:78)
    at com.sun.javafx.collections.VetoableObservableList.callObservers(VetoableObservableList.java:65)
    at com.sun.javafx.collections.ObservableListWrapper.add(ObservableListWrapper.java:97)
    at com.sun.javafx.collections.VetoableObservableList.add(VetoableObservableList.java:147)
    at com.sun.javafx.collections.ObservableListWrapper.add(ObservableListWrapper.java:90)
    at com.javafx.experiments.scenicview.ScenicView.storeTarget(ScenicView.java:307)
    at com.javafx.experiments.scenicview.ScenicView.setTarget(ScenicView.java:271)
    at com.javafx.experiments.scenicview.ScenicView.<init>(ScenicView.java:263)
    at com.javafx.experiments.scenicview.ScenicView.show(ScenicView.java:64)
    at com.javafx.experiments.scenicview.ScenicView.show(ScenicView.java:56)
    ... 13 more