javax.swing.undo.CannotUndoException
   at javax.swing.undo.AbstractUndoableEdit.undo(AbstractUndoableEdit.java:93)
   at javax.swing.undo.CompoundEdit.undo(CompoundEdit.java:42)
   at org.netbeans.editor.BaseDocument$AtomicCompoundEdit.undo(BaseDocument.java:2202)
   at org.netbeans.editor.BaseDocument.breakAtomicLock(BaseDocument.java:1864)
   at org.netbeans.editor.GuardedDocument.runAtomicAsUser(GuardedDocument.java:350)
   at org.netbeans.editor.BaseKit$InsertBreakAction.actionPerformed(BaseKit.java:1201)
   at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:339)
   at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1633)
   at javax.swing.JComponent.processKeyBinding(JComponent.java:2851)
   at javax.swing.JComponent.processKeyBindings(JComponent.java:2886)
   at javax.swing.JComponent.processKeyEvent(JComponent.java:2814)
   at java.awt.Component.processEvent(Component.java:6040)
   at java.awt.Container.processEvent(Container.java:2041)
   at java.awt.Component.dispatchEventImpl(Component.java:4630)
   at java.awt.Container.dispatchEventImpl(Container.java:2099)
   at java.awt.Component.dispatchEvent(Component.java:4460)
   at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1850)
   at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:712)
   at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:990)
   at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:855)
   at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:676)
   at java.awt.Component.dispatchEventImpl(Component.java:4502)
   at java.awt.Container.dispatchEventImpl(Container.java:2099)
   at java.awt.Window.dispatchEventImpl(Window.java:2478)
   at java.awt.Component.dispatchEvent(Component.java:4460)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:137)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)