I have closed Netbeans with a property file in Editor 
opened. After that i have deleted this file. Opening 
Netbeans again causes now the following Exception:

Wed May 22 13:46:27 CEST 2002: 
java.lang.NullPointerException: <no message>
java.lang.NullPointerException
        at 
org.netbeans.modules.properties.PropertiesOpen$PropertiesCl
oneableTopComponent.getUndoRedo(PropertiesOpen.java:695)
        at org.openide.actions.UndoAction.getUndoRedo
(UndoAction.java:91)
        at 
org.openide.actions.UndoAction$Listener.propertyChange
(UndoAction.java:139)
        at 
org.openide.util.WeakListener$PropertyChange.propertyChange
(WeakListener.java:325)
        at 
java.beans.PropertyChangeSupport.firePropertyChange
(PropertyChangeSupport.java:152)
        at 
org.netbeans.core.windows.RegistryImpl.tryFireChanges
(RegistryImpl.java:358)
        at 
org.netbeans.core.windows.RegistryImpl.selectedNodesChanged
(RegistryImpl.java:318)
        at 
org.netbeans.core.windows.frames.DefaultContainerImpl.doAct
ivateComponent(DefaultContainerImpl.java:564)
        at 
org.netbeans.core.windows.frames.DefaultContainerImpl.react
ivateSelectedComponent(DefaultContainerImpl.java:730)
        at 
org.netbeans.core.windows.frames.SplitContainerImpl.stateCh
anged(SplitContainerImpl.java:629)
        at javax.swing.JTabbedPane.fireStateChanged
(JTabbedPane.java:234)
        at 
javax.swing.JTabbedPane$ModelListener.stateChanged
(JTabbedPane.java:179)
        at 
javax.swing.DefaultSingleSelectionModel.fireStateChanged
(DefaultSingleSelectionModel.java:99)
        at 
javax.swing.DefaultSingleSelectionModel.setSelectedIndex
(DefaultSingleSelectionModel.java:51)
        at javax.swing.JTabbedPane.setSelectedIndex
(JTabbedPane.java:349)
        at 
javax.swing.plaf.basic.BasicTabbedPaneUI$MouseHandler.mouse
Pressed(BasicTabbedPaneUI.java:1822)
        at java.awt.AWTEventMulticaster.mousePressed
(AWTEventMulticaster.java:220)
        at java.awt.AWTEventMulticaster.mousePressed
(AWTEventMulticaster.java:220)
        at java.awt.Component.processMouseEvent
(Component.java:3712)
        at java.awt.Component.processEvent
(Component.java:3544)
        at java.awt.Container.processEvent
(Container.java:1164)
        at java.awt.Component.dispatchEventImpl
(Component.java:2593)
        at java.awt.Container.dispatchEventImpl
(Container.java:1213)
        at java.awt.Component.dispatchEvent
(Component.java:2497)
        at 
java.awt.LightweightDispatcher.retargetMouseEvent
(Container.java:2451)
        at java.awt.LightweightDispatcher.processMouseEvent
(Container.java:2210)
        at java.awt.LightweightDispatcher.dispatchEvent
(Container.java:2125)
        at java.awt.Container.dispatchEventImpl
(Container.java:1200)
        at java.awt.Window.dispatchEventImpl
(Window.java:926)
        at java.awt.Component.dispatchEvent
(Component.java:2497)
[catch] at java.awt.EventQueue.dispatchEvent
(EventQueue.java:339)
        at 
java.awt.EventDispatchThread.pumpOneEventForHierarchy
(EventDispatchThread.java:131)
        at 
java.awt.EventDispatchThread.pumpEventsForHierarchy
(EventDispatchThread.java:98)
        at java.awt.EventDispatchThread.pumpEvents
(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run
(EventDispatchThread.java:85)