java.lang.NullPointerException
        at org.netbeans.spi.project.ui.support.NodeFactorySupport$DelegateChildren.addNotify(NodeFactorySupport.java:176)
        at org.openide.nodes.Children.callAddNotify(Children.java:541)
        at org.openide.nodes.Children.getArray(Children.java:583)
        at org.openide.nodes.Children.getNodes(Children.java:422)
        at org.openide.nodes.FilterNode$ChildrenAdapter.run(FilterNode.java:1501)
        at org.openide.nodes.FilterNode$Children.updateKeys(FilterNode.java:1455)
        at org.openide.nodes.FilterNode$Children.addNotifyImpl(FilterNode.java:1348)
        at org.openide.nodes.FilterNode$Children.addNotify(FilterNode.java:1340)
        at org.openide.nodes.Children.callAddNotify(Children.java:541)
        at org.openide.nodes.Children.getArray(Children.java:583)
        at org.openide.nodes.Children.getNodes(Children.java:422)
        at org.openide.explorer.view.VisualizerNode.getChildren(VisualizerNode.java:244)
        at org.openide.explorer.view.VisualizerNode.getChildCount(VisualizerNode.java:290)
        at javax.swing.tree.DefaultTreeModel.getChildCount(DefaultTreeModel.java:168)
        at javax.swing.tree.VariableHeightLayoutCache$TreeStateNode.expand(VariableHeightLayoutCache.java:1461)
        at javax.swing.tree.VariableHeightLayoutCache$TreeStateNode.expand(VariableHeightLayoutCache.java:1270)
        at javax.swing.tree.VariableHeightLayoutCache.ensurePathIsExpanded(VariableHeightLayoutCache.java:966)
        at javax.swing.tree.VariableHeightLayoutCache.setExpandedState(VariableHeightLayoutCache.java:164)
        at javax.swing.plaf.basic.BasicTreeUI.updateExpandedDescendants(BasicTreeUI.java:1648)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.treeExpanded(BasicTreeUI.java:3721)
        at javax.swing.JTree.fireTreeExpanded(JTree.java:2659)
        at javax.swing.JTree.setExpandedState(JTree.java:3430)
        at javax.swing.JTree.expandPath(JTree.java:2166)
        at javax.swing.plaf.basic.BasicTreeUI.toggleExpandState(BasicTreeUI.java:2209)
        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$Handler.handleSelection(BasicTreeUI.java:3508)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressedDND(BasicTreeUI.java:3494)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressed(BasicTreeUI.java:3453)
        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:6038)
        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:3983)
        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)