出异常了 希望大神们看看什么情况

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
        {
            this.listView1.Items.Clear();
            if (e.Node.Tag != null)
            {
                string folderPath = e.Node.ToString();
                DirectoryInfo folder = new DirectoryInfo(folderPath);
                FileInfo[] files = null;
                try
                {
                    files = folder.GetFiles();
                }
                catch(UnauthorizedAccessException)
                {

 
                }
                if (files != null)
                {
                    foreach (FileInfo file in files)
                    {
                        listView1.Items.Add(new ListViewItem(new string[]
                        {
                            file.Name,
                            "文件",
                            GetFileSize(file),
                            file.LastWriteTime.ToString()
                        }));
                    }
                }
            }
        }