jtree对空文件夹的显示问题

import java.io.File;
import java.util.Iterator;
import java.util.Vector;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.JTree;
import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreePath;

public class FileTreeFrame extends JFrame {
private JTree fileTree;

private FileSystemModel fileSystemModel;

private JTextArea fileDetailsTextArea = new JTextArea();

public FileTreeFrame(String directory) {
super("JTree FileSystem Viewer");
fileDetailsTextArea.setEditable(false);
fileSystemModel = new FileSystemModel(new File(directory));
fileTree = new J