java.lang.NullPointerException
   at org.openide.text.UndoRedoManager.setPerformingSaveActions(UndoRedoManager.java:224)
   at org.openide.text.CloneableEditorSupport.saveDocument(CloneableEditorSupport.java:1137)
   at org.openide.text.DataEditorSupport.superSaveDoc(DataEditorSupport.java:606)
   at org.openide.text.DataEditorSupport$SaveImpl.run(DataEditorSupport.java:1304)
   at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:127)
   at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:607)
   at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:603)
   at org.openide.text.DataEditorSupport.saveDocument(DataEditorSupport.java:602)
   at org.netbeans.modules.csl.core.GsfDataObject$GenericEditorSupport$Environment$SaveSupport.save(GsfDataObject.java:220)
   at org.netbeans.modules.css.model.api.Model$4.run(Model.java:464)
   at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
   at java.awt.EventQueue.access$200(EventQueue.java:103)
   at java.awt.EventQueue$3.run(EventQueue.java:682)
   at java.awt.EventQueue$3.run(EventQueue.java:680)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:158)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)