java.lang.NullPointerException
        at org.netbeans.lib.lexer.inc.TokenListUpdater.update(TokenListUpdater.java:263)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.updateTokenListByModification(TokenHierarchyUpdate.java:338)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate$TLLInfo.update(TokenHierarchyUpdate.java:507)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.processLevelInfos(TokenHierarchyUpdate.java:314)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.update(TokenHierarchyUpdate.java:143)
        at org.netbeans.lib.lexer.TokenHierarchyOperation.textModified(TokenHierarchyOperation.java:429)
        at org.netbeans.spi.lexer.TokenHierarchyControl.textModified(TokenHierarchyControl.java:99)
        at org.netbeans.lib.lexer.inc.DocumentInput.modified(DocumentInput.java:153)
        at org.netbeans.lib.lexer.inc.DocumentInput.removeUpdate(DocumentInput.java:144)
        at org.netbeans.lib.editor.util.swing.PriorityDocumentListenerList.removeUpdate(PriorityDocumentListenerList.java:85)
        at javax.swing.text.AbstractDocument.fireRemoveUpdate(AbstractDocument.java:243)
        at org.netbeans.editor.BaseDocument.fireRemoveUpdate(BaseDocument.java:1390)
        at org.netbeans.editor.BaseDocumentEvent.undo(BaseDocumentEvent.java:310)
        at org.netbeans.editor.GuardedDocumentEvent.undo(GuardedDocumentEvent.java:69)
        at javax.swing.undo.CompoundEdit.undo(CompoundEdit.java:46)
        at org.netbeans.editor.BaseDocument$AtomicCompoundEdit.undo(BaseDocument.java:1806)
        at org.openide.text.CloneableEditorSupport$FilterUndoableEdit.undo(CloneableEditorSupport.java:2652)
        at org.openide.text.CloneableEditorSupport$BeforeModificationEdit.undo(CloneableEditorSupport.java:2806)
        at javax.swing.undo.UndoManager.undoTo(UndoManager.java:320)
        at javax.swing.undo.UndoManager.undo(UndoManager.java:398)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.access$2601(CloneableEditorSupport.java:2838)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.run(CloneableEditorSupport.java:2978)
        at org.netbeans.editor.GuardedDocument.runAtomic(GuardedDocument.java:251)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:2958)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:2950)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.undo(CloneableEditorSupport.java:2869)
        at org.openide.actions.UndoAction.performAction(UndoAction.java:170)
        at org.openide.util.actions.CallableSystemAction$1.run(CallableSystemAction.java:118)
        at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:77)
        at org.openide.util.actions.CallableSystemAction.actionPerformed(CallableSystemAction.java:114)
        at org.netbeans.modules.editor.NbEditorKit$NbUndoAction.actionPerformed(NbEditorKit.java:554)
        at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:290)
        at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1636)
        at javax.swing.JComponent.processKeyBinding(JComponent.java:2849)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2884)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2812)
        at java.awt.Component.processEvent(Component.java:5818)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4413)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4243)
        at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1848)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:697)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:962)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:834)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:661)
        at java.awt.Component.dispatchEventImpl(Component.java:4285)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Window.dispatchEventImpl(Window.java:2440)
        at java.awt.Component.dispatchEvent(Component.java:4243)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)