java.lang.AssertionError
        at org.netbeans.lib.lexer.inc.TokenListUpdater.update(TokenListUpdater.java:128)
        at org.netbeans.lib.lexer.TokenHierarchyOperation.addNestedChanges(TokenHierarchyOperation.java:311)
        at org.netbeans.lib.lexer.TokenHierarchyOperation.textModified(TokenHierarchyOperation.java:275)
        at org.netbeans.spi.lexer.TokenHierarchyControl.textModified(TokenHierarchyControl.java:81)
        at org.netbeans.lib.lexer.inc.DocumentInput.modified(DocumentInput.java:117)
        at org.netbeans.lib.lexer.inc.DocumentInput.removeUpdate(DocumentInput.java:108)
        at org.netbeans.lib.editor.util.swing.PriorityDocumentListenerList.removeUpdate(PriorityDocumentListenerList.java:63)
        at javax.swing.text.AbstractDocument.fireRemoveUpdate(AbstractDocument.java:242)
        at org.netbeans.editor.BaseDocument.fireRemoveUpdate(BaseDocument.java:1381)
        at org.netbeans.editor.BaseDocumentEvent.undo(BaseDocumentEvent.java:269)
        at org.netbeans.editor.GuardedDocumentEvent.undo(GuardedDocumentEvent.java:47)
        at javax.swing.undo.CompoundEdit.undo(CompoundEdit.java:46)
        at org.netbeans.editor.BaseDocument$AtomicCompoundEdit.undo(BaseDocument.java:1771)
        at org.openide.text.CloneableEditorSupport$FilterUndoableEdit.undo(CloneableEditorSupport.java:2537)
        at org.openide.text.CloneableEditorSupport$BeforeModificationEdit.undo(CloneableEditorSupport.java:2691)
        at javax.swing.undo.UndoManager.undoTo(UndoManager.java:210)
        at javax.swing.undo.UndoManager.undo(UndoManager.java:275)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.access$2101(CloneableEditorSupport.java:2723)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.run(CloneableEditorSupport.java:2863)
        at org.netbeans.editor.GuardedDocument.runAtomic(GuardedDocument.java:230)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:2843)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:2835)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.undo(CloneableEditorSupport.java:2754)
        at org.openide.actions.UndoAction.performAction(UndoAction.java:148)
        at org.openide.util.actions.CallableSystemAction$1.run(CallableSystemAction.java:96)
        at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:55)
        at org.openide.util.actions.CallableSystemAction.actionPerformed(CallableSystemAction.java:92)
        at org.netbeans.modules.editor.NbEditorKit$NbUndoAction.actionPerformed(NbEditorKit.java:522)
        at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:261)
        at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1571)
        at javax.swing.JComponent.processKeyBinding(JComponent.java:2730)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2765)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2693)
        at java.awt.Component.processEvent(Component.java:5265)
        at java.awt.Container.processEvent(Container.java:1966)
        at java.awt.Component.dispatchEventImpl(Component.java:3955)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1810)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:668)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:916)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:794)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:632)
        at java.awt.Component.dispatchEventImpl(Component.java:3841)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Window.dispatchEventImpl(Window.java:1766)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
[catch] at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:234)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)