NPE when closing nifty gui preview

What steps will reproduce the problem?
1. Open a Nifty GUI XML preview window by double clicking the file, then close 
it.
2. An exception will appear (see below)

Nifty XML files or rest of exception can be provided on request.

java.lang.NullPointerException
at de.lessvoid.nifty.screen.Screen.resetLayers(Screen.java:244)
at de.lessvoid.nifty.screen.Screen.endScreen(Screen.java:227)
at de.lessvoid.nifty.Nifty.exit(Nifty.java:667)
at 
com.jme3.gde.gui.multiview.NiftyPreviewPanel.cleanup(NiftyPreviewPanel.java:239)
at 
com.jme3.gde.gui.multiview.PreviewToolbarElement.componentClosed(PreviewToolbarE
lement.java:45)
at 
org.netbeans.core.multiview.MultiViewPeer.peerComponentClosed(MultiViewPeer.java
:252)
at 
org.netbeans.core.multiview.MultiViewCloneableTopComponent.componentClosed(Multi
ViewCloneableTopComponent.java:120)
[catch] at 
org.openide.windows.WindowManager.componentCloseNotify(WindowManager.java:322)
at 
org.netbeans.core.windows.WindowManagerImpl.notifyTopComponentClosed(WindowManag
erImpl.java:1113)
at org.netbeans.core.windows.Central.removeModeTopComponent(Central.java:1007)
at org.netbeans.core.windows.Central.userClosedTopComponent(Central.java:1978)

Original issue reported on code.google.com by ShadowIs...@gmail.com on 1 Aug 2011 at 3:42

Parinesh-Baitule / jmonkeyengine

NPE when closing nifty gui preview #371