com.sun.jdi.VMDisconnectedException: connection is closed
        at com.sun.tools.jdi.TargetVM.send(TargetVM.java:274)
        at com.sun.tools.jdi.VirtualMachineImpl.sendToTarget(VirtualMachineImpl.java:1011)
        at com.sun.tools.jdi.PacketStream.send(PacketStream.java:41)
        at com.sun.tools.jdi.JDWP$ThreadGroupReference$Parent.enqueueCommand(JDWP.java:5840)
        at com.sun.tools.jdi.JDWP$ThreadGroupReference$Parent.process(JDWP.java:5826)
        at com.sun.tools.jdi.ThreadGroupReferenceImpl.parent(ThreadGroupReferenceImpl.java:60)
        at org.netbeans.modules.debugger.jpda.models.JPDAThreadGroupImpl.getParentThreadGroup(JPDAThreadGroupImpl.java:75)
        at org.netbeans.modules.debugger.jpda.ui.models.DebuggingTreeModel.getTopLevelThreadsAndGroups(DebuggingTreeModel.java:198)
        at org.netbeans.modules.debugger.jpda.ui.models.DebuggingTreeModel.computeChildren(DebuggingTreeModel.java:126)
        at org.netbeans.modules.debugger.jpda.ui.models.CachedChildrenTreeModel.recomputeChildren(CachedChildrenTreeModel.java:122)
        at org.netbeans.modules.debugger.jpda.ui.models.CachedChildrenTreeModel.recomputeChildren(CachedChildrenTreeModel.java:113)
        at org.netbeans.modules.debugger.jpda.ui.models.DebuggingTreeModel.fireNodeChanged(DebuggingTreeModel.java:278)
        at org.netbeans.modules.debugger.jpda.ui.models.DebuggingTreeModel$DebuggingPreferenceChangeListener.preferenceChange(DebuggingTreeModel.java:650)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:0)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.openide.util.WeakListenerImpl$ProxyListener.invoke(WeakListenerImpl.java:449)
        at $Proxy10.preferenceChange(.java:0)
        at java.util.prefs.AbstractPreferences$EventDispatchThread.run(AbstractPreferences.java:1475)