Build: NetBeans IDE Dev (Build 20110414-e4828c5494d2)
VM: Java HotSpot(TM) Client VM, 19.1-b02, Java(TM) SE Runtime Environment, 1.6.0_24-b07
OS: Linux

Stacktrace: 
java.lang.AssertionError: c = org.netbeans.modules.apisupport.project.ui.platform.NbPlatformCustomizerSources$ListListener tree.sym = org.netbeans.modules.apisupport.project.ui.platform.NbPlatformCustomizerSources.ListListener tree = 
static abstract class ListListener implements ListDataListener, ListSelectionListener {
    
    ListListener() {
        super();
    }
    
    public void intervalAdded(final ListDataEvent e) {
        listChanged();
    }
    
    public void intervalRemoved(final ListDataEvent e) {
        listChanged();
    }
    
    public void contentsChanged(final ListDataEvent e) {
        listChanged();
    }
    
    public void valueChanged(final ListSelectionEvent e) {
        if (!e.getValueIsAdjusting()) {
            listChanged();
        }
    }
    
    abstract void listChanged();
}
   at com.sun.tools.javac.util.Assert.error(Assert.java:133)
   at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:3239)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3218)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3167)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3149)
   at com.sun.tools.javac.comp.Attr.visitClassDef(Attr.java:720)