java.lang.NullPointerException
   at org.netbeans.modules.editor.hints.AnnotationHolder.removeUpdate(AnnotationHolder.java:412)
   at org.netbeans.lib.editor.util.swing.PriorityDocumentListenerList.removeUpdate(PriorityDocumentListenerList.java:99)
   at javax.swing.text.AbstractDocument.fireRemoveUpdate(AbstractDocument.java:0)
   at org.netbeans.editor.BaseDocument.fireRemoveUpdate(BaseDocument.java:1634)
   at org.netbeans.editor.BaseDocumentEvent.undo(BaseDocumentEvent.java:291)
   at org.netbeans.editor.GuardedDocumentEvent.undo(GuardedDocumentEvent.java:69)
   at javax.swing.undo.CompoundEdit.undo(CompoundEdit.java:0)
   at org.netbeans.editor.BaseDocument$AtomicCompoundEdit.undo(BaseDocument.java:2164)
   at org.openide.text.CloneableEditorSupport$FilterUndoableEdit.undo(CloneableEditorSupport.java:2994)
   at org.openide.text.CloneableEditorSupport$BeforeModificationEdit.undo(CloneableEditorSupport.java:3154)
   at javax.swing.undo.UndoManager.undoTo(UndoManager.java:0)
   at javax.swing.undo.UndoManager.undo(UndoManager.java:0)
   at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.access$3201(CloneableEditorSupport.java:3187)
   at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.run(CloneableEditorSupport.java:3360)
   at org.netbeans.editor.GuardedDocument.runAtomic(GuardedDocument.java:311)
   at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:3336)
   at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:3327)
   at org.openide.text.CloneableEditorSupport$CESUndoRedoManager$RenderUndo.<init>(CloneableEditorSupport.java:3323)
   at org.openide.text.CloneableEditorSupport$CESUndoRedoManager.undo(CloneableEditorSupport.java:3220)
   at org.openide.actions.UndoAction.performAction(UndoAction.java:177)
   at org.openide.util.actions.CallableSystemAction$1.run(CallableSystemAction.java:126)
   at org.openide.util.actions.ActionInvoker$1.run(ActionInvoker.java:92)
   at org.openide.util.actions.ActionInvoker.doPerformAction(ActionInvoker.java:113)
   at org.openide.util.actions.ActionInvoker.invokeAction(ActionInvoker.java:96)
   at org.openide.util.actions.CallableSystemAction.actionPerformed(CallableSystemAction.java:123)
   at org.netbeans.modules.editor.NbEditorKit$NbUndoAction.actionPerformed(NbEditorKit.java:549)
   at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:336)
   at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:0)
   at javax.swing.JComponent.processKeyBinding(JComponent.java:0)
   at javax.swing.JComponent.processKeyBindings(JComponent.java:0)
   at javax.swing.JComponent.processKeyEvent(JComponent.java:0)
   at java.awt.Component.processEvent(Component.java:0)
   at java.awt.Container.processEvent(Container.java:0)
   at java.awt.Component.dispatchEventImpl(Component.java:0)
   at java.awt.Container.dispatchEventImpl(Container.java:0)
   at java.awt.Component.dispatchEvent(Component.java:0)
   at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:0)
   at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:0)
   at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:0)
   at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:0)
   at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:0)
   at java.awt.Component.dispatchEventImpl(Component.java:0)
   at java.awt.Container.dispatchEventImpl(Container.java:0)
   at java.awt.Window.dispatchEventImpl(Window.java:0)
   at java.awt.Component.dispatchEvent(Component.java:0)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:0)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:133)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:0)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:0)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:0)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:0)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:0)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:0)