java.lang.NullPointerException
        at javax.swing.CellRendererPane.addImpl(CellRendererPane.java:85)
        at java.awt.Container.add(Container.java:351)
        at javax.swing.plaf.basic.BasicListUI.updateLayoutState(BasicListUI.java:1156)
        at javax.swing.plaf.basic.BasicListUI.maybeUpdateLayoutState(BasicListUI.java:1105)
        at javax.swing.plaf.basic.BasicListUI.getPreferredSize(BasicListUI.java:356)
        at javax.swing.JComponent.getPreferredSize(JComponent.java:1624)
        at java.awt.BorderLayout.preferredLayoutSize(BorderLayout.java:690)
        at java.awt.Container.preferredSize(Container.java:1558)
        at java.awt.Container.getPreferredSize(Container.java:1543)
        at javax.swing.JComponent.getPreferredSize(JComponent.java:1626)
        at javax.swing.ScrollPaneLayout.layoutContainer(ScrollPaneLayout.java:769)
        at java.awt.Container.layout(Container.java:1401)
        at java.awt.Container.doLayout(Container.java:1390)
        at java.awt.Container.validateTree(Container.java:1473)
        at java.awt.Container.validate(Container.java:1448)
        at javax.swing.RepaintManager.validateInvalidComponents(RepaintManager.java:379)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:113)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)