java.lang.NullPointerException
        at org.netbeans.core.windows.Central.userClosedTopComponent(Central.java:1919)
        at org.netbeans.core.windows.view.DefaultView.userClosedTopComponent(DefaultView.java:741)
        at org.netbeans.core.windows.view.ui.TabbedHandler.actionPerformed(TabbedHandler.java:319)
        at org.netbeans.core.windows.view.ui.slides.TabbedSlideAdapter.postActionEvent(TabbedSlideAdapter.java:151)
        at org.netbeans.core.windows.view.ui.slides.CommandManager.postEvent(CommandManager.java:411)
        at org.netbeans.core.windows.view.ui.slides.CommandManager.actionPerformed(CommandManager.java:240)
        at org.netbeans.swing.tabcontrol.TabbedContainer.postActionEvent(TabbedContainer.java:680)
        at org.netbeans.swing.tabcontrol.TabbedContainerUI.shouldPerformAction(TabbedContainerUI.java:162)
        at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI.access$2700(DefaultTabbedContainerUI.java:109)
        at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI$DisplayerActionListener.actionPerformed(DefaultTabbedContainerUI.java:1258)
        at org.netbeans.swing.tabcontrol.TabDisplayer.postActionEvent(TabDisplayer.java:543)
        at org.netbeans.swing.tabcontrol.TabDisplayerUI.shouldPerformAction(TabDisplayerUI.java:176)
        at org.netbeans.swing.tabcontrol.TabDisplayerUI.postTabAction(TabDisplayerUI.java:233)
        at org.netbeans.swing.tabcontrol.plaf.TabControlButton.performAction(TabControlButton.java:196)
        at org.netbeans.swing.tabcontrol.plaf.TabControlButton.fireActionPerformed(TabControlButton.java:187)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
        at java.awt.Component.processMouseEvent(Component.java:6041)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5806)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4413)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4243)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4322)
        at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:3986)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:3916)
        at java.awt.Container.dispatchEventImpl(Container.java:2102)
        at java.awt.Window.dispatchEventImpl(Window.java:2440)
        at java.awt.Component.dispatchEvent(Component.java:4243)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)