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.getBounds(FixedHeightLayoutCache.java:176)
        at javax.swing.plaf.basic.BasicTreeUI.getPathBounds(BasicTreeUI.java:515)
        at javax.swing.plaf.basic.BasicTreeUI.getPathBounds(BasicTreeUI.java:508)
        at com.sun.java.swing.plaf.windows.WindowsTreeUI.ensureRowsAreVisible(WindowsTreeUI.java:72)
        at javax.swing.plaf.basic.BasicTreeUI.toggleExpandState(BasicTreeUI.java:2213)
        at javax.swing.plaf.basic.BasicTreeUI.handleExpandControlClick(BasicTreeUI.java:2196)
        at javax.swing.plaf.basic.BasicTreeUI.checkForClickInExpandControl(BasicTreeUI.java:2154)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.handleSelection(BasicTreeUI.java:3516)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressedDND(BasicTreeUI.java:3502)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressed(BasicTreeUI.java:3461)
        at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
        at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
        at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
        at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
        at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
        at java.awt.Component.processMouseEvent(Component.java:6131)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5899)
        at java.awt.Container.processEvent(Container.java:2023)
        at java.awt.Component.dispatchEventImpl(Component.java:4501)
        at java.awt.Container.dispatchEventImpl(Container.java:2081)
        at java.awt.Component.dispatchEvent(Component.java:4331)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4301)
        at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:3962)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:3895)
        at java.awt.Container.dispatchEventImpl(Container.java:2067)
        at java.awt.Window.dispatchEventImpl(Window.java:2458)
        at java.awt.Component.dispatchEvent(Component.java:4331)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)