java.lang.NullPointerException
        at javax.swing.AbstractButton.removeNotify(AbstractButton.java:1013)
        at javax.swing.JButton.removeNotify(JButton.java:217)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at javax.swing.JRootPane.removeNotify(JRootPane.java:750)
        at java.awt.Container.removeNotify(Container.java:2619)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.removeNotify(Container.java:2619)
        at javax.swing.JComponent.removeNotify(JComponent.java:4699)
        at java.awt.Container.remove(Container.java:1136)
        at java.awt.Container.remove(Container.java:1203)
        at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI$ModelListener.indicesChanged(DefaultTabbedContainerUI.java:1215)
        at org.netbeans.swing.tabcontrol.DefaultTabDataModel.fireIndicesChanged(DefaultTabDataModel.java:492)
        at org.netbeans.swing.tabcontrol.DefaultTabDataModel.setTabs(DefaultTabDataModel.java:120)
        at org.netbeans.core.windows.view.ui.tabcontrol.TabbedAdapter.setTopComponents(TabbedAdapter.java:234)
        at org.netbeans.core.windows.view.ui.TabbedHandler.setTopComponents(TabbedHandler.java:157)
        at org.netbeans.core.windows.view.ui.AbstractModeContainer.setTopComponents(AbstractModeContainer.java:124)
        at org.netbeans.core.windows.view.ModeView.setTopComponents(ModeView.java:137)
        at org.netbeans.core.windows.view.ViewHierarchy.updateViewForAccessor(ViewHierarchy.java:254)
        at org.netbeans.core.windows.view.ViewHierarchy.updateViewForAccessor(ViewHierarchy.java:241)
        at org.netbeans.core.windows.view.ViewHierarchy.updateViewForAccessor(ViewHierarchy.java:226)
        at org.netbeans.core.windows.view.ViewHierarchy.updateViewHierarchy(ViewHierarchy.java:143)
        at org.netbeans.core.windows.view.DefaultView.changeGUI(DefaultView.java:149)
        at org.netbeans.core.windows.ViewRequestor.dispatchRequest(ViewRequestor.java:269)
        at org.netbeans.core.windows.ViewRequestor.processRequest(ViewRequestor.java:245)
        at org.netbeans.core.windows.ViewRequestor.postRequest(ViewRequestor.java:183)
        at org.netbeans.core.windows.ViewRequestor.scheduleRequest(ViewRequestor.java:123)
        at org.netbeans.core.windows.Central.removeModeTopComponent(Central.java:952)
        at org.netbeans.core.windows.Central.userClosedTopComponent(Central.java:1929)
        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.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.plaf.BasicTabDisplayerUI.access$1500(BasicTabDisplayerUI.java:116)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.performCommand(BasicTabDisplayerUI.java:715)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.potentialCommand(BasicTabDisplayerUI.java:700)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.mouseReleased(BasicTabDisplayerUI.java:748)
        at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
        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)