java.lang.NullPointerException
        at javax.swing.plaf.synth.SynthTreeUI.paint(SynthTreeUI.java:302)
        at javax.swing.plaf.synth.SynthTreeUI.update(SynthTreeUI.java:205)
        at javax.swing.JComponent.paintComponent(JComponent.java:763)
        at javax.swing.JComponent.paint(JComponent.java:1027)
        at javax.swing.JComponent.paintToOffscreen(JComponent.java:5122)
        at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:285)
        at javax.swing.RepaintManager.paint(RepaintManager.java:1128)
        at javax.swing.JComponent._paintImmediately(JComponent.java:5070)
        at javax.swing.JComponent.paintImmediately(JComponent.java:4880)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:723)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:679)
        at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:659)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:128)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        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)