java.lang.NullPointerException
        at org.openide.nodes.CookieSet.add(CookieSet.java:54)
        at org.netbeans.modules.java.ui.nodes.elements.ElementNode.<init>(ElementNode.java:114)
        at org.netbeans.modules.java.ui.nodes.elements.ClassNode.<init>(ClassNode.java:76)
        at org.netbeans.modules.java.tools.OverridePanel2$Ch.createNodes(OverridePanel2.java:338)
        at org.openide.nodes.Children$Keys$KE.nodes(Children.java:1971)
        at org.openide.nodes.ChildrenArray.nodesFor(ChildrenArray.java:112)
        at org.openide.nodes.Children$Info.nodes(Children.java:1068)
        at org.openide.nodes.Children.updateAdd(Children.java:876)
        at org.openide.nodes.Children.setEntries(Children.java:663)
        at org.openide.nodes.Children$4.run(Children.java:1862)
        at org.openide.util.Mutex.postRequest(Mutex.java:971)
        at org.openide.util.Mutex.postWriteRequest(Mutex.java:422)
        at org.openide.nodes.Children$Keys.applyKeys(Children.java:1870)
        at org.openide.nodes.Children$Keys.setKeys(Children.java:1829)
        at org.netbeans.modules.java.tools.OverridePanel2$Ch.update(OverridePanel2.java:375)
        at org.netbeans.modules.java.tools.OverridePanel2$Ch.actionPerformed(OverridePanel2.java:360)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
        at javax.swing.JToggleButton$ToggleButtonModel.setPressed(JToggleButton.java:269)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:234)
        at java.awt.Component.processMouseEvent(Component.java:5488)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3093)
        at java.awt.Component.processEvent(Component.java:5253)
        at java.awt.Container.processEvent(Container.java:1966)
        at java.awt.Component.dispatchEventImpl(Component.java:3955)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4212)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3892)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3822)
        at java.awt.Container.dispatchEventImpl(Container.java:2010)
        at java.awt.Window.dispatchEventImpl(Window.java:1766)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
[catch] at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:234)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:153)
        at java.awt.Dialog$1.run(Dialog.java:515)
        at java.awt.Dialog.show(Dialog.java:536)
        at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:780)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:823)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:811)
        at org.openide.util.Mutex.doEventAccess(Mutex.java:1028)
        at org.openide.util.Mutex.readAccess(Mutex.java:167)
        at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:796)
        at org.netbeans.modules.java.tools.OverrideAction.performAction(OverrideAction.java:93)
        at org.openide.util.actions.NodeAction$3.run(NodeAction.java:440)
        at org.openide.util.actions.CallableSystemAction.doPerformAction(CallableSystemAction.java:116)
        at org.openide.util.actions.NodeAction$DelegateAction.actionPerformed(NodeAction.java:438)
        at org.openide.windows.TopComponent.processKeyBinding(TopComponent.java:695)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2776)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2693)
        at java.awt.Component.processEvent(Component.java:5265)
        at java.awt.Container.processEvent(Container.java:1966)
        at java.awt.Component.dispatchEventImpl(Component.java:3955)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1810)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:668)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:916)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:794)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:632)
        at java.awt.Component.dispatchEventImpl(Component.java:3841)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Window.dispatchEventImpl(Window.java:1766)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:234)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)