diff --git a/v2rayN/v2rayN/App.xaml.cs b/v2rayN/v2rayN/App.xaml.cs
index 76a2e041..8a30a4fa 100644
--- a/v2rayN/v2rayN/App.xaml.cs
+++ b/v2rayN/v2rayN/App.xaml.cs
@@ -84,7 +84,7 @@ namespace v2rayN
             }
         }
 
-        private void TaskScheduler_UnobservedTaskException(object sender, UnobservedTaskExceptionEventArgs e)
+        private void TaskScheduler_UnobservedTaskException(object? sender, UnobservedTaskExceptionEventArgs e)
         {
             Utils.SaveLog("TaskScheduler_UnobservedTaskException", e.Exception);
         }
diff --git a/v2rayN/v2rayN/Handler/CoreConfigHandler.cs b/v2rayN/v2rayN/Handler/CoreConfigHandler.cs
index 40a49e33..7dc8319b 100644
--- a/v2rayN/v2rayN/Handler/CoreConfigHandler.cs
+++ b/v2rayN/v2rayN/Handler/CoreConfigHandler.cs
@@ -828,11 +828,11 @@ namespace v2rayN.Handler
         /// <param name="fileName"></param>
         /// <param name="msg"></param>
         /// <returns></returns>
-        private static int GenerateClientCustomConfig(ProfileItem node, string fileName, out string msg)
+        private static int GenerateClientCustomConfig(ProfileItem node, string? fileName, out string msg)
         {
             try
             {
-                if (node == null)
+                if (node == null || fileName is null)
                 {
                     msg = ResUI.CheckServerSettings;
                     return -1;
diff --git a/v2rayN/v2rayN/Handler/SpeedtestHandler.cs b/v2rayN/v2rayN/Handler/SpeedtestHandler.cs
index 8e22454e..d477d1ec 100644
--- a/v2rayN/v2rayN/Handler/SpeedtestHandler.cs
+++ b/v2rayN/v2rayN/Handler/SpeedtestHandler.cs
@@ -243,7 +243,7 @@ namespace v2rayN.Handler
 
                 WebProxy webProxy = new(Global.Loopback, it.port);
 
-                await downloadHandle.DownloadDataAsync(url, webProxy, timeout, async (bool success, string msg) =>
+                await downloadHandle.DownloadDataAsync(url, webProxy, timeout, (bool success, string msg) =>
                 {
                     decimal.TryParse(msg, out decimal dec);
                     if (dec > 0)
@@ -294,7 +294,7 @@ namespace v2rayN.Handler
                 if (item is null) continue;
 
                 WebProxy webProxy = new(Global.Loopback, it.port);
-                _ = downloadHandle.DownloadDataAsync(url, webProxy, timeout, async (bool success, string msg) =>
+                _ = downloadHandle.DownloadDataAsync(url, webProxy, timeout, (bool success, string msg) =>
                 {
                     decimal.TryParse(msg, out decimal dec);
                     if (dec > 0)
diff --git a/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs b/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs
index dd9f0526..e7cc6376 100644
--- a/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs
+++ b/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs
@@ -917,8 +917,8 @@ namespace v2rayN.ViewModels
 
         public void AddServerViaClipboard()
         {
-            string clipboardData = Utils.GetClipboardData();
-            int ret = ConfigHandler.AddBatchServers(ref _config, clipboardData, _subId, false);
+            var clipboardData = Utils.GetClipboardData();
+            int ret = ConfigHandler.AddBatchServers(ref _config, clipboardData!, _subId, false);
             if (ret > 0)
             {
                 InitSubscriptionView();