diff --git a/v2rayN/v2rayUpgrade/MainForm.cs b/v2rayN/v2rayUpgrade/MainForm.cs
index 6b9ff16c..fe2ee592 100644
--- a/v2rayN/v2rayUpgrade/MainForm.cs
+++ b/v2rayN/v2rayUpgrade/MainForm.cs
@@ -11,18 +11,22 @@ namespace v2rayUpgrade
     public partial class MainForm : Form
     {
         private readonly string defaultFilename = "v2ray-windows.zip";
-        private string fileName;
+        private string? fileName;
 
         public MainForm(string[] args)
         {
             InitializeComponent();
             if (args.Length > 0)
             {
-                fileName = string.Join(" ", args);
-                fileName = HttpUtility.UrlDecode(fileName);
+                fileName = HttpUtility.UrlDecode(string.Join(" ", args));
+            }
+            else
+            {
+                fileName = defaultFilename;
             }
         }
-        private void showWarn(string message)
+
+        private void ShowWarn(string message)
         {
             MessageBox.Show(message, "", MessageBoxButtons.OK, MessageBoxIcon.Warning);
         }
@@ -34,7 +38,7 @@ namespace v2rayUpgrade
                 Process[] existing = Process.GetProcessesByName("v2rayN");
                 foreach (Process p in existing)
                 {
-                    string path = p.MainModule.FileName;
+                    string? path = p.MainModule?.FileName;
                     if (path == GetPath("v2rayN.exe"))
                     {
                         p.Kill();
@@ -45,72 +49,67 @@ namespace v2rayUpgrade
             catch (Exception ex)
             {
                 // Access may be denied without admin right. The user may not be an administrator.
-                showWarn("Failed to close v2rayN(关闭v2rayN失败).\n" +
+                ShowWarn("Failed to close v2rayN(关闭v2rayN失败).\n" +
                     "Close it manually, or the upgrade may fail.(请手动关闭正在运行的v2rayN，否则可能升级失败。\n\n" + ex.StackTrace);
             }
 
-            StringBuilder sb = new StringBuilder();
-            try
+            if (!File.Exists(fileName))
             {
-                if (!File.Exists(fileName))
+                if (File.Exists(defaultFilename))
                 {
-                    if (File.Exists(defaultFilename))
-                    {
-                        fileName = defaultFilename;
-                    }
-                    else
-                    {
-                        showWarn("Upgrade Failed, File Not Exist(升级失败,文件不存在).");
-                        return;
-                    }
+                    fileName = defaultFilename;
                 }
+                else
+                {
+                    ShowWarn("Upgrade Failed, File Not Exist(升级失败,文件不存在).");
+                    return;
+                }
+            }
 
-                string thisAppOldFile = Application.ExecutablePath + ".tmp";
+            StringBuilder sb = new();
+            try
+            {
+                string thisAppOldFile = $"{Application.ExecutablePath}.tmp";
                 File.Delete(thisAppOldFile);
                 string startKey = "v2rayN/";
 
-
-                using (ZipArchive archive = ZipFile.OpenRead(fileName))
+                using ZipArchive archive = ZipFile.OpenRead(fileName);
+                foreach (ZipArchiveEntry entry in archive.Entries)
                 {
-                    foreach (ZipArchiveEntry entry in archive.Entries)
+                    try
                     {
-                        try
+                        if (entry.Length == 0)
                         {
-                            if (entry.Length == 0)
-                            {
-                                continue;
-                            }
-                            string fullName = entry.FullName;
-                            if (fullName.StartsWith(startKey))
-                            {
-                                fullName = fullName.Substring(startKey.Length, fullName.Length - startKey.Length);
-                            }
-                            if (Application.ExecutablePath.ToLower() == GetPath(fullName).ToLower())
-                            {
-                                File.Move(Application.ExecutablePath, thisAppOldFile);
-                            }
-
-                            string entryOuputPath = GetPath(fullName);
-
-                            FileInfo fileInfo = new FileInfo(entryOuputPath);
-                            fileInfo.Directory.Create();
-                            entry.ExtractToFile(entryOuputPath, true);
+                            continue;
                         }
-                        catch (Exception ex)
+                        string fullName = entry.FullName;
+                        if (fullName.StartsWith(startKey))
                         {
-                            sb.Append(ex.StackTrace);
+                            fullName = fullName[startKey.Length..];
                         }
+                        if (string.Equals(Application.ExecutablePath, GetPath(fullName), StringComparison.OrdinalIgnoreCase))
+                        {
+                            File.Move(Application.ExecutablePath, thisAppOldFile);
+                        }
+
+                        string entryOuputPath = GetPath(fullName);
+                        Directory.CreateDirectory(Path.GetDirectoryName(entryOuputPath) ?? "");
+                        entry.ExtractToFile(entryOuputPath, true);
+                    }
+                    catch (Exception ex)
+                    {
+                        sb.Append(ex.StackTrace);
                     }
                 }
             }
             catch (Exception ex)
             {
-                showWarn("Upgrade Failed(升级失败)." + ex.StackTrace);
+                ShowWarn("Upgrade Failed(升级失败)." + ex.StackTrace);
                 return;
             }
             if (sb.Length > 0)
             {
-                showWarn("Upgrade Failed,Hold ctrl + c to copy to clipboard.\n" +
+                ShowWarn("Upgrade Failed,Hold ctrl + c to copy to clipboard.\n" +
                     "(升级失败,按住ctrl+c可以复制到剪贴板)." + sb.ToString());
                 return;
             }
diff --git a/v2rayN/v2rayUpgrade/v2rayUpgrade.csproj b/v2rayN/v2rayUpgrade/v2rayUpgrade.csproj
index 835420ba..40ddb328 100644
--- a/v2rayN/v2rayUpgrade/v2rayUpgrade.csproj
+++ b/v2rayN/v2rayUpgrade/v2rayUpgrade.csproj
@@ -6,5 +6,6 @@
 	<Copyright>Copyright © 2019-2023 (GPLv3)</Copyright>
 	<FileVersion>1.1.0.0</FileVersion>
 	<ApplicationManifest>app.manifest</ApplicationManifest>
+	<Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>
\ No newline at end of file