java.lang.AssertionError
        at org.netbeans.lib.lexer.TokenHierarchyUpdate$TLLInfo.markRemoved(TokenHierarchyUpdate.java:382)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.markRemovedEmbeddings(TokenHierarchyUpdate.java:279)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.processNonBoundsChange(TokenHierarchyUpdate.java:222)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.processChange(TokenHierarchyUpdate.java:142)
        at org.netbeans.lib.lexer.TokenHierarchyUpdate.update(TokenHierarchyUpdate.java:113)
        at org.netbeans.lib.lexer.TokenHierarchyOperation.textModified(TokenHierarchyOperation.java:323)
        at org.netbeans.spi.lexer.TokenHierarchyControl.textModified(TokenHierarchyControl.java:81)
        at org.netbeans.lib.lexer.inc.DocumentInput.modified(DocumentInput.java:125)
        at org.netbeans.lib.lexer.inc.DocumentInput.removeUpdate(DocumentInput.java:113)
        at org.netbeans.lib.editor.util.swing.PriorityDocumentListenerList.removeUpdate(PriorityDocumentListenerList.java:63)
        at javax.swing.text.AbstractDocument.fireRemoveUpdate(AbstractDocument.java:242)
        at org.netbeans.editor.BaseDocument.fireRemoveUpdate(BaseDocument.java:1345)
        at org.netbeans.editor.BaseDocumentEvent.undo(BaseDocumentEvent.java:288)
        at org.netbeans.editor.GuardedDocumentEvent.undo(GuardedDocumentEvent.java:47)
        at javax.swing.undo.CompoundEdit.undo(CompoundEdit.java:46)
        at org.netbeans.editor.BaseDocument$AtomicCompoundEdit.undo(BaseDocument.java:1741)
        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$2101(CloneableEditorSupport.java:2722)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.run(CloneableEditorSupport.java:2862)
        at org.netbeans.editor.GuardedDocument.runAtomic(GuardedDocument.java:229)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:2842)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:2834)
        at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.undo(CloneableEditorSupport.java:2753)
        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:532)
        at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:266)
        at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1576)
        at javax.swing.JComponent.processKeyBinding(JComponent.java:2763)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2798)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2726)
        at java.awt.Component.processEvent(Component.java:5331)
        at java.awt.Container.processEvent(Container.java:2010)
        at java.awt.Component.dispatchEventImpl(Component.java:4021)
        at java.awt.Container.dispatchEventImpl(Container.java:2068)
        at java.awt.Component.dispatchEvent(Component.java:3869)
        at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1810)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:672)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:920)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:798)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:636)
        at java.awt.Component.dispatchEventImpl(Component.java:3907)
        at java.awt.Container.dispatchEventImpl(Container.java:2068)
        at java.awt.Window.dispatchEventImpl(Window.java:1774)
        at java.awt.Component.dispatchEvent(Component.java:3869)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
[catch] at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)