java.lang.AssertionError: tn must be our child!
        at org.openide.explorer.view.VisualizerChildren.recomputeIndexes(VisualizerChildren.java:94)
        at org.openide.explorer.view.VisualizerChildren.getIndex(VisualizerChildren.java:161)
        at org.openide.explorer.view.VisualizerNode.getIndex(VisualizerNode.java:276)
        at javax.swing.tree.DefaultTreeModel.getIndexOfChild(DefaultTreeModel.java:142)
        at javax.swing.tree.FixedHeightLayoutCache.getVisiblePathsFrom(FixedHeightLayoutCache.java:269)
        at javax.swing.plaf.basic.BasicTreeUI.paint(BasicTreeUI.java:1122)
        at javax.swing.plaf.metal.MetalTreeUI.paint(MetalTreeUI.java:152)
        at javax.swing.plaf.ComponentUI.update(ComponentUI.java:142)
        at javax.swing.JComponent.paintComponent(JComponent.java:743)
        at javax.swing.JComponent.paint(JComponent.java:1006)
        at org.openide.explorer.view.TreeView$ExplorerTree.access$1201(TreeView.java:1557)
        at org.openide.explorer.view.TreeView$ExplorerTree.guardedPaint(TreeView.java:1746)
        at org.openide.explorer.view.TreeView$ExplorerTree.access$1600(TreeView.java:1557)
        at org.openide.explorer.view.TreeView$ExplorerTree$GuardedActions.run(TreeView.java:2084)
        at org.openide.util.Mutex.readAccess(Mutex.java:285)
        at org.openide.explorer.view.TreeView$ExplorerTree$GuardedActions.<init>(TreeView.java:2077)
        at org.openide.explorer.view.TreeView$ExplorerTree.paint(TreeView.java:1681)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JViewport.paint(JViewport.java:728)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at org.netbeans.swing.tabcontrol.TabbedContainer.paint(TabbedContainer.java:968)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at org.netbeans.core.windows.view.ui.MultiSplitPane.paint(MultiSplitPane.java:323)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JLayeredPane.paint(JLayeredPane.java:559)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paint(JComponent.java:1015)
        at javax.swing.JLayeredPane.paint(JLayeredPane.java:559)
        at javax.swing.JComponent.paintChildren(JComponent.java:843)
        at javax.swing.JComponent.paintWithOffscreenBuffer(JComponent.java:4979)
        at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:4925)
        at javax.swing.JComponent.paint(JComponent.java:996)
        at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:21)
        at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:60)
        at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:97)
        at java.awt.Container.paint(Container.java:1709)
        at org.netbeans.core.windows.view.ui.MainWindow.paint(MainWindow.java:577)
        at sun.awt.RepaintArea.paintComponent(RepaintArea.java:248)
        at sun.awt.X11.XRepaintArea.paintComponent(XRepaintArea.java:56)
        at sun.awt.RepaintArea.paint(RepaintArea.java:224)
        at sun.awt.X11.XComponentPeer.handleEvent(XComponentPeer.java:645)
        at java.awt.Component.dispatchEventImpl(Component.java:4060)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Window.dispatchEventImpl(Window.java:1791)
        at java.awt.Component.dispatchEvent(Component.java:3819)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        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)