java.lang.reflect.InvocationTargetException
        at sun.reflect.GeneratedMethodAccessor86.invoke(GeneratedMethodAccessor86.java:0)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.openide.util.WeakListenerImpl$ListenerReference.run(WeakListenerImpl.java:584)
        at org.openide.util.Utilities$ActiveQueue.run(Utilities.java:3119)
        at java.lang.Thread.run(Thread.java:619)
java.lang.IllegalStateException: Node has been removed.
        at java.util.prefs.AbstractPreferences.removePreferenceChangeListener(AbstractPreferences.java:1034)
        at sun.reflect.GeneratedMethodAccessor86.invoke(GeneratedMethodAccessor86.java:0)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.openide.util.WeakListenerImpl$ListenerReference.run(WeakListenerImpl.java:584)
        at org.openide.util.Utilities$ActiveQueue.run(Utilities.java:3119)
        at java.lang.Thread.run(Thread.java:619)