Thread: application Task problem - updating JTree

Hi all , i am running to a problem , maybe one of you can find the problem .
i have a JTree , and i want to update him in a Thread , since i want it to change the progress bar .
i used the Netbeans progress bar .
everything works fine , my only problem is , that once the Task is done , i see the JTree return to be empty .
and not saving the root i add in the succeeded function .
the code :

// this is the button i press to add to start the Task
    @Action public Task  AddToList(){
        Task newTask = new runThreadFolderBrowser(getApplication());
        return newTask;
    }
 
  private class runThreadFolderBrowser extends org.jdesktop.application.Task<Object, Void> {
         private DefaultMutableTreeNode saveTreeNode;
           // <editor-fold defaultstate="collapsed" desc="Constructor of the Class">
         runThreadFolderBrowser(org.jdesktop.application.Application app){
             // the Constructor Runs on EDT , and can Update the GUI
             super(app);
             treeComponents.setEditable(true);
         } 
         @Override protected Object doInBackground(){
             CheckListItem[] allFoldersItems =  BackupServerSettings.Instance.researchBackupFolder();
             DefaultMutableTreeNode rootNode  = new DefaultMutableTreeNode("Backup Server");
             try {
               succeeded(rootNode);
                return null;
             } catch ( NullPointerException noFolder_noConnection){
                return null;
             }
         }
 
         @Override protected void succeeded(Object rootNode){
             DefaultTreeModel treemodel = (DefaultTreeModel) treeComponents.getModel(); // get the current JTree
             treemodel.setRoot((DefaultMutableTreeNode)rootNode);  // change the Root folders of the current tree .
             treeComponents.setRootVisible(true);
             treeComponents.repaint(); // repaint the JTree
         }
 
         @Override protected void finished(){
         }
     }

ok , so problem is solved .
i had to change the return from null to rootNode , in the doIn Background function .
but thanks .