unable to run sample

[knziha]

type E:\ and enter:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
	at sample.DirectoryTreeCellFormater.register(DirectoryTreeCellFormater.java:40)
	at sample.DirectoryTreeFactory.call(DirectoryTreeFactory.java:16)
	at sample.DirectoryTreeFactory.call(DirectoryTreeFactory.java:1)
	at com.sun.javafx.scene.control.skin.TreeViewSkin.createCell(TreeViewSkin.java:230)
	at com.sun.javafx.scene.control.skin.TreeViewSkin.lambda$new$535(TreeViewSkin.java:72)
	at com.sun.javafx.scene.control.skin.VirtualFlow.getAvailableCell(VirtualFlow.java:2031)
	at com.sun.javafx.scene.control.skin.VirtualFlow.addLeadingCells(VirtualFlow.java:1245)
	at com.sun.javafx.scene.control.skin.VirtualFlow.layoutChildren(VirtualFlow.java:1194)
	at javafx.scene.Parent.layout(Parent.java:1087)
	at javafx.scene.Parent.layout(Parent.java:1093)
	at javafx.scene.Parent.layout(Parent.java:1093)
	at javafx.scene.Scene.doLayoutPass(Scene.java:552)
	at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2397)
	at com.sun.javafx.tk.Toolkit.lambda$runPulse$29(Toolkit.java:398)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:397)
	at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:424)
	at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:518)
	at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:498)
	at com.sun.javafx.tk.quantum.QuantumToolkit.pulseFromQueue(QuantumToolkit.java:491)
	at com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$403(QuantumToolkit.java:319)
	at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
	at java.lang.Thread.run(Unknown Source)