diff --git a/v2rayN/v2rayN/Handler/ConfigHandler.cs b/v2rayN/v2rayN/Handler/ConfigHandler.cs
index b99f507f..59e1bc5e 100644
--- a/v2rayN/v2rayN/Handler/ConfigHandler.cs
+++ b/v2rayN/v2rayN/Handler/ConfigHandler.cs
@@ -205,7 +205,7 @@ namespace v2rayN.Handler
 
             }
 
-            LazyConfig.Instance.SetConfig(ref config);
+            LazyConfig.Instance.SetConfig(config);
             return 0;
         }
         /// <summary>
@@ -438,7 +438,7 @@ namespace v2rayN.Handler
         /// <param name="config"></param>
         /// <param name="item"></param>
         /// <returns></returns>
-        public static int SetDefaultServerIndex(ref Config config, string indexId)
+        public static int SetDefaultServerIndex(ref Config config, string? indexId)
         {
             if (Utils.IsNullOrEmpty(indexId))
             {
@@ -460,7 +460,7 @@ namespace v2rayN.Handler
                 return 0;
             }
             var allItems = LazyConfig.Instance.ProfileItemIndexs("");
-            if (allItems.Where(t => t == config.indexId).Count() > 0)
+            if (allItems.Where(t => t == config.indexId).Any())
             {
                 return 0;
             }
@@ -468,13 +468,13 @@ namespace v2rayN.Handler
             {
                 return SetDefaultServerIndex(ref config, lstProfile[0].indexId);
             }
-            if (allItems.Count() > 0)
+            if (allItems.Count > 0)
             {
                 return SetDefaultServerIndex(ref config, allItems.FirstOrDefault());
             }
             return -1;
         }
-        public static ProfileItem GetDefaultServer(ref Config config)
+        public static ProfileItem? GetDefaultServer(ref Config config)
         {
             var item = LazyConfig.Instance.GetProfileItem(config.indexId);
             if (item is null)
@@ -1041,7 +1041,7 @@ namespace v2rayN.Handler
 
             ProfileItem profileItem = new();
             //Is v2ray configuration
-            V2rayConfig v2rayConfig = Utils.FromJson<V2rayConfig>(clipboardData);
+            V2rayConfig? v2rayConfig = Utils.FromJson<V2rayConfig>(clipboardData);
             if (v2rayConfig != null
                 && v2rayConfig.inbounds != null
                 && v2rayConfig.inbounds.Count > 0
@@ -1176,7 +1176,7 @@ namespace v2rayN.Handler
 
         public static int AddBatchServers(ref Config config, string clipboardData, string subid, bool isSub)
         {
-            List<ProfileItem> lstOriSub = null;
+            List<ProfileItem>? lstOriSub = null;
             if (isSub && !Utils.IsNullOrEmpty(subid))
             {
                 lstOriSub = LazyConfig.Instance.ProfileItems(subid);
diff --git a/v2rayN/v2rayN/Handler/CoreConfigHandler.cs b/v2rayN/v2rayN/Handler/CoreConfigHandler.cs
index be92a35b..1dc417fd 100644
--- a/v2rayN/v2rayN/Handler/CoreConfigHandler.cs
+++ b/v2rayN/v2rayN/Handler/CoreConfigHandler.cs
@@ -25,7 +25,7 @@ namespace v2rayN.Handler
         /// <param name="msg"></param>
         /// <param name="content"></param>
         /// <returns></returns>
-        public static int GenerateClientConfig(ProfileItem node, string fileName, out string msg, out string content)
+        public static int GenerateClientConfig(ProfileItem node, string? fileName, out string msg, out string content)
         {
             content = string.Empty;
             try
@@ -43,7 +43,7 @@ namespace v2rayN.Handler
                 }
                 else
                 {
-                    V2rayConfig v2rayConfig = null;
+                    V2rayConfig? v2rayConfig = null;
                     if (GenerateClientConfigContent(node, false, ref v2rayConfig, out msg) != 0)
                     {
                         return -1;
@@ -114,11 +114,11 @@ namespace v2rayN.Handler
             {
                 v2rayConfig.inbounds = new List<Inbounds>();
 
-                Inbounds inbound = GetInbound(config.inbound[0], Global.InboundSocks, 0, true);
+                Inbounds? inbound = GetInbound(config.inbound[0], Global.InboundSocks, 0, true);
                 v2rayConfig.inbounds.Add(inbound);
 
                 //http
-                Inbounds inbound2 = GetInbound(config.inbound[0], Global.InboundHttp, 1, false);
+                Inbounds? inbound2 = GetInbound(config.inbound[0], Global.InboundHttp, 1, false);
                 v2rayConfig.inbounds.Add(inbound2);
 
                 if (config.inbound[0].allowLANConn)
@@ -157,7 +157,7 @@ namespace v2rayN.Handler
             return 0;
         }
 
-        private static Inbounds GetInbound(InItem inItem, string tag, int offset, bool bSocks)
+        private static Inbounds? GetInbound(InItem inItem, string tag, int offset, bool bSocks)
         {
             string result = Utils.GetEmbedText(Global.v2raySampleInbound);
             if (Utils.IsNullOrEmpty(result))
@@ -957,7 +957,7 @@ namespace v2rayN.Handler
             return 0;
         }
 
-        public static int GenerateClientConfigContent(ProfileItem node, bool blExport, ref V2rayConfig v2rayConfig, out string msg)
+        public static int GenerateClientConfigContent(ProfileItem node, bool blExport, ref V2rayConfig? v2rayConfig, out string msg)
         {
             try
             {
@@ -1034,7 +1034,7 @@ namespace v2rayN.Handler
                     return -1;
                 }
 
-                V2rayConfig v2rayConfig = Utils.FromJson<V2rayConfig>(result);
+                V2rayConfig? v2rayConfig = Utils.FromJson<V2rayConfig>(result);
                 if (v2rayConfig == null)
                 {
                     msg = ResUI.FailedGenDefaultConfiguration;
@@ -1123,7 +1123,7 @@ namespace v2rayN.Handler
 
         #region Import (export) client/server configuration
 
-        public static ProfileItem ImportFromClientConfig(string fileName, out string msg)
+        public static ProfileItem? ImportFromClientConfig(string fileName, out string msg)
         {
             msg = string.Empty;
             ProfileItem profileItem = new ProfileItem();
@@ -1137,7 +1137,7 @@ namespace v2rayN.Handler
                     return null;
                 }
 
-                V2rayConfig v2rayConfig = Utils.FromJson<V2rayConfig>(result);
+                V2rayConfig? v2rayConfig = Utils.FromJson<V2rayConfig>(result);
                 if (v2rayConfig == null)
                 {
                     msg = ResUI.FailedConversionConfiguration;
@@ -1262,7 +1262,7 @@ namespace v2rayN.Handler
             return profileItem;
         }
 
-        public static ProfileItem ImportFromServerConfig(string fileName, out string msg)
+        public static ProfileItem? ImportFromServerConfig(string fileName, out string msg)
         {
             msg = string.Empty;
             ProfileItem profileItem = new ProfileItem();
@@ -1276,7 +1276,7 @@ namespace v2rayN.Handler
                     return null;
                 }
 
-                V2rayConfig v2rayConfig = Utils.FromJson<V2rayConfig>(result);
+                V2rayConfig? v2rayConfig = Utils.FromJson<V2rayConfig>(result);
                 if (v2rayConfig == null)
                 {
                     msg = ResUI.FailedConversionConfiguration;
@@ -1401,7 +1401,7 @@ namespace v2rayN.Handler
 
         public static int Export2ClientConfig(ProfileItem node, string fileName, out string msg)
         {
-            V2rayConfig v2rayConfig = null;
+            V2rayConfig? v2rayConfig = null;
             if (GenerateClientConfigContent(node, true, ref v2rayConfig, out msg) != 0)
             {
                 return -1;
@@ -1440,7 +1440,7 @@ namespace v2rayN.Handler
                     return "";
                 }
 
-                V2rayConfig v2rayConfig = Utils.FromJson<V2rayConfig>(result);
+                V2rayConfig? v2rayConfig = Utils.FromJson<V2rayConfig>(result);
                 if (v2rayConfig == null)
                 {
                     msg = ResUI.FailedGenDefaultConfiguration;
@@ -1523,7 +1523,7 @@ namespace v2rayN.Handler
                     v2rayConfig.inbounds.Add(inbound);
 
                     //outbound
-                    V2rayConfig v2rayConfigCopy = Utils.FromJson<V2rayConfig>(result);
+                    V2rayConfig? v2rayConfigCopy = Utils.FromJson<V2rayConfig>(result);
                     var item = LazyConfig.Instance.GetProfileItem(it.indexId);
                     if (item is null)
                     {
diff --git a/v2rayN/v2rayN/Handler/CoreHandler.cs b/v2rayN/v2rayN/Handler/CoreHandler.cs
index f5ac0957..87d7f063 100644
--- a/v2rayN/v2rayN/Handler/CoreHandler.cs
+++ b/v2rayN/v2rayN/Handler/CoreHandler.cs
@@ -12,9 +12,9 @@ namespace v2rayN.Handler
     class CoreHandler
     {
         private static string _coreCConfigRes = Global.coreConfigFileName;
-        private CoreInfo _coreInfo;
+        private CoreInfo? _coreInfo;
         private int _processId = 0;
-        private Process _process;
+        private Process? _process;
         Action<bool, string> _updateFunc;
 
         public CoreHandler(Action<bool, string> update)
@@ -108,7 +108,7 @@ namespace v2rayN.Handler
                         Process[] existing = Process.GetProcessesByName(vName);
                         foreach (Process p in existing)
                         {
-                            string path = p.MainModule.FileName;
+                            string? path = p.MainModule?.FileName;
                             if (path == $"{Utils.GetBinPath(vName, _coreInfo.coreType)}.exe")
                             {
                                 KillProcess(p);
@@ -193,7 +193,7 @@ namespace v2rayN.Handler
                 {
                     p.OutputDataReceived += (sender, e) =>
                     {
-                        if (!String.IsNullOrEmpty(e.Data))
+                        if (!string.IsNullOrEmpty(e.Data))
                         {
                             string msg = e.Data + Environment.NewLine;
                             ShowMsg(false, msg);
diff --git a/v2rayN/v2rayN/Handler/DownloadHandle.cs b/v2rayN/v2rayN/Handler/DownloadHandle.cs
index caa463ea..66fb7316 100644
--- a/v2rayN/v2rayN/Handler/DownloadHandle.cs
+++ b/v2rayN/v2rayN/Handler/DownloadHandle.cs
@@ -16,7 +16,7 @@ namespace v2rayN.Handler
     {
         public event EventHandler<ResultEventArgs> UpdateCompleted;
 
-        public event ErrorEventHandler Error;
+        public event ErrorEventHandler? Error;
 
 
         public class ResultEventArgs : EventArgs
@@ -99,7 +99,7 @@ namespace v2rayN.Handler
             }
         }
 
-        public async Task<string> UrlRedirectAsync(string url, bool blProxy)
+        public async Task<string?> UrlRedirectAsync(string url, bool blProxy)
         {
             Utils.SetSecurityProtocol(LazyConfig.Instance.GetConfig().guiItem.enableSecurityProtocolTls13);
             var webRequestHandler = new SocketsHttpHandler
@@ -112,7 +112,7 @@ namespace v2rayN.Handler
             HttpResponseMessage response = await client.GetAsync(url);
             if (response.StatusCode.ToString() == "Redirect")
             {
-                return response.Headers.Location.ToString();
+                return response.Headers.Location?.ToString();
             }
             else
             {
@@ -121,7 +121,7 @@ namespace v2rayN.Handler
             }
         }
 
-        public async Task<string> TryDownloadString(string url, bool blProxy, string userAgent)
+        public async Task<string?> TryDownloadString(string url, bool blProxy, string userAgent)
         {
             try
             {
@@ -161,14 +161,12 @@ namespace v2rayN.Handler
 
             try
             {
-                using (var wc = new WebClient())
+                using var wc = new WebClient();
+                wc.Proxy = GetWebProxy(blProxy);
+                var result3 = await wc.DownloadStringTaskAsync(url);
+                if (!Utils.IsNullOrEmpty(result3))
                 {
-                    wc.Proxy = GetWebProxy(blProxy);
-                    var result3 = await wc.DownloadStringTaskAsync(url);
-                    if (!Utils.IsNullOrEmpty(result3))
-                    {
-                        return result3;
-                    }
+                    return result3;
                 }
             }
             catch (Exception ex)
@@ -189,7 +187,7 @@ namespace v2rayN.Handler
         /// DownloadString
         /// </summary> 
         /// <param name="url"></param>
-        public async Task<string> DownloadStringAsync(string url, bool blProxy, string userAgent)
+        public async Task<string?> DownloadStringAsync(string url, bool blProxy, string userAgent)
         {
             try
             {
@@ -234,7 +232,7 @@ namespace v2rayN.Handler
         /// DownloadString
         /// </summary> 
         /// <param name="url"></param>
-        public async Task<string> DownloadStringViaDownloader(string url, bool blProxy, string userAgent)
+        public async Task<string?> DownloadStringViaDownloader(string url, bool blProxy, string userAgent)
         {
             try
             {
@@ -262,7 +260,7 @@ namespace v2rayN.Handler
         }
 
 
-        public int RunAvailabilityCheck(WebProxy webProxy)
+        public int RunAvailabilityCheck(WebProxy? webProxy)
         {
             try
             {
@@ -324,7 +322,7 @@ namespace v2rayN.Handler
             return msg;
         }
 
-        private WebProxy GetWebProxy(bool blProxy)
+        private WebProxy? GetWebProxy(bool blProxy)
         {
             if (!blProxy)
             {
@@ -341,7 +339,7 @@ namespace v2rayN.Handler
 
         private bool SocketCheck(string ip, int port)
         {
-            Socket sock = null;
+            Socket? sock = null;
             try
             {
                 IPAddress ipa = IPAddress.Parse(ip);
diff --git a/v2rayN/v2rayN/Handler/LazyConfig.cs b/v2rayN/v2rayN/Handler/LazyConfig.cs
index f1fe5093..f0947dbf 100644
--- a/v2rayN/v2rayN/Handler/LazyConfig.cs
+++ b/v2rayN/v2rayN/Handler/LazyConfig.cs
@@ -22,7 +22,7 @@ namespace v2rayN.Handler
 
         #region Config
 
-        public void SetConfig(ref Config config)
+        public void SetConfig(Config config)
         {
             _config = config;
         }
@@ -118,7 +118,7 @@ namespace v2rayN.Handler
             return SqliteHelper.Instance.Query<ProfileItemModel>(sql).ToList();
         }
 
-        public ProfileItem GetProfileItem(string indexId)
+        public ProfileItem? GetProfileItem(string indexId)
         {
             if (Utils.IsNullOrEmpty(indexId))
             {
@@ -173,7 +173,7 @@ namespace v2rayN.Handler
             return item.coreType;
         }
 
-        public CoreInfo GetCoreInfo(ECoreType coreType)
+        public CoreInfo? GetCoreInfo(ECoreType coreType)
         {
             if (coreInfos == null)
             {
@@ -182,7 +182,7 @@ namespace v2rayN.Handler
             return coreInfos.Where(t => t.coreType == coreType).FirstOrDefault();
         }
 
-        public List<CoreInfo> GetCoreInfos()
+        public List<CoreInfo>? GetCoreInfos()
         {
             if (coreInfos == null)
             {
diff --git a/v2rayN/v2rayN/Handler/MainFormHandler.cs b/v2rayN/v2rayN/Handler/MainFormHandler.cs
index 96c15478..9c942757 100644
--- a/v2rayN/v2rayN/Handler/MainFormHandler.cs
+++ b/v2rayN/v2rayN/Handler/MainFormHandler.cs
@@ -82,7 +82,7 @@ namespace v2rayN.Handler
             return BitmapFrame.Create(new Uri($"pack://application:,,,/Resources/NotifyIcon{index}.ico", UriKind.RelativeOrAbsolute));
         }
 
-        private Icon GetNotifyIcon4Routing(Config config)
+        private Icon? GetNotifyIcon4Routing(Config config)
         {
             try
             {
@@ -286,7 +286,7 @@ namespace v2rayN.Handler
             BackupGuiNConfig(config, true);
 
             config = resConfig;
-            LazyConfig.Instance.SetConfig(ref config);
+            LazyConfig.Instance.SetConfig(config);
 
             return true;
         }
diff --git a/v2rayN/v2rayN/Handler/ProxySetting.cs b/v2rayN/v2rayN/Handler/ProxySetting.cs
index 045f6039..446b1caa 100644
--- a/v2rayN/v2rayN/Handler/ProxySetting.cs
+++ b/v2rayN/v2rayN/Handler/ProxySetting.cs
@@ -10,7 +10,7 @@ namespace v2rayN.Handler
             return SetProxy(null, null, 1);
         }
 
-        public static bool SetProxy(string strProxy, string exceptions, int type)
+        public static bool SetProxy(string? strProxy, string? exceptions, int type)
         {
             InternetPerConnOptionList list = new InternetPerConnOptionList();
 
@@ -189,8 +189,8 @@ namespace v2rayN.Handler
         //判断是否使用代理
         public static bool UsedProxy()
         {
-            using RegistryKey rk = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Internet Settings", true);
-            if (rk.GetValue("ProxyEnable").ToString() == "1")
+            using RegistryKey? rk = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Internet Settings", true);
+            if (rk?.GetValue("ProxyEnable")?.ToString() == "1")
             {
                 return true;
             }
@@ -202,7 +202,7 @@ namespace v2rayN.Handler
         //获得代理的IP和端口
         public static string GetProxyProxyServer()
         {
-            using RegistryKey rk = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Internet Settings", true);
+            using RegistryKey? rk = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Internet Settings", true);
             string ProxyServer = rk.GetValue("ProxyServer").ToString();
             return ProxyServer;
 
diff --git a/v2rayN/v2rayN/Handler/QRCodeHelper.cs b/v2rayN/v2rayN/Handler/QRCodeHelper.cs
index 643b7e7e..ff5528d2 100644
--- a/v2rayN/v2rayN/Handler/QRCodeHelper.cs
+++ b/v2rayN/v2rayN/Handler/QRCodeHelper.cs
@@ -9,7 +9,7 @@ namespace v2rayN.Handler
     /// </summary>
     public class QRCodeHelper
     {
-        public static DrawingImage GetQRCode(string strContent)
+        public static DrawingImage? GetQRCode(string strContent)
         {
             try
             {
diff --git a/v2rayN/v2rayN/Handler/ShareHandler.cs b/v2rayN/v2rayN/Handler/ShareHandler.cs
index ed93607b..d76b201b 100644
--- a/v2rayN/v2rayN/Handler/ShareHandler.cs
+++ b/v2rayN/v2rayN/Handler/ShareHandler.cs
@@ -17,7 +17,7 @@ namespace v2rayN.Handler
         /// </summary>
         /// <param name="item"></param>
         /// <returns></returns>
-        public static string GetShareUrl(ProfileItem item)
+        public static string? GetShareUrl(ProfileItem item)
         {
             try
             {
@@ -167,7 +167,7 @@ namespace v2rayN.Handler
             return Utils.IsIpv6(address) ? $"[{address}]" : address;
         }
 
-        private static int GetStdTransport(ProfileItem item, string securityDef, ref Dictionary<string, string> dicQuery)
+        private static int GetStdTransport(ProfileItem item, string? securityDef, ref Dictionary<string, string> dicQuery)
         {
             if (!Utils.IsNullOrEmpty(item.flow))
             {
@@ -270,7 +270,7 @@ namespace v2rayN.Handler
         /// </summary>
         /// <param name="msg"></param>
         /// <returns></returns>
-        public static ProfileItem ImportFromClipboardConfig(string clipboardData, out string msg)
+        public static ProfileItem? ImportFromClipboardConfig(string clipboardData, out string msg)
         {
             msg = string.Empty;
             ProfileItem profileItem = new ProfileItem();
@@ -357,7 +357,7 @@ namespace v2rayN.Handler
             return profileItem;
         }
 
-        private static ProfileItem ResolveVmess(string result, out string msg)
+        private static ProfileItem? ResolveVmess(string result, out string msg)
         {
             msg = string.Empty;
             var profileItem = new ProfileItem
@@ -369,7 +369,7 @@ namespace v2rayN.Handler
             result = Utils.Base64Decode(result);
 
             //转成Json
-            VmessQRCode vmessQRCode = Utils.FromJson<VmessQRCode>(result);
+            VmessQRCode? vmessQRCode = Utils.FromJson<VmessQRCode>(result);
             if (vmessQRCode == null)
             {
                 msg = ResUI.FailedConversionConfiguration;
@@ -407,17 +407,17 @@ namespace v2rayN.Handler
             return profileItem;
         }
 
-        private static ProfileItem ResolveVmess4Kitsunebi(string result)
+        private static ProfileItem? ResolveVmess4Kitsunebi(string result)
         {
             ProfileItem profileItem = new ProfileItem
             {
                 configType = EConfigType.VMess
             };
-            result = result.Substring(Global.vmessProtocol.Length);
+            result = result[Global.vmessProtocol.Length..];
             int indexSplit = result.IndexOf("?");
             if (indexSplit > 0)
             {
-                result = result.Substring(0, indexSplit);
+                result = result[..indexSplit];
             }
             result = Utils.Base64Decode(result);
 
@@ -445,7 +445,7 @@ namespace v2rayN.Handler
             return profileItem;
         }
 
-        private static ProfileItem ResolveStdVmess(string result)
+        private static ProfileItem? ResolveStdVmess(string result)
         {
             ProfileItem i = new ProfileItem
             {
@@ -526,7 +526,7 @@ namespace v2rayN.Handler
             return i;
         }
 
-        private static ProfileItem ResolveSip002(string result)
+        private static ProfileItem? ResolveSip002(string result)
         {
             Uri parsedUrl;
             try
@@ -545,7 +545,7 @@ namespace v2rayN.Handler
             };
             string rawUserInfo = parsedUrl.GetComponents(UriComponents.UserInfo, UriFormat.UriEscaped);
             //2022-blake3
-            if (rawUserInfo.Contains(":"))
+            if (rawUserInfo.Contains(':'))
             {
                 string[] userInfoParts = rawUserInfo.Split(new[] { ':' }, 2);
                 if (userInfoParts.Length != 2)
@@ -589,10 +589,10 @@ namespace v2rayN.Handler
             return server;
         }
 
-        private static readonly Regex UrlFinder = new Regex(@"ss://(?<base64>[A-Za-z0-9+-/=_]+)(?:#(?<tag>\S+))?", RegexOptions.IgnoreCase);
-        private static readonly Regex DetailsParser = new Regex(@"^((?<method>.+?):(?<password>.*)@(?<hostname>.+?):(?<port>\d+?))$", RegexOptions.IgnoreCase);
+        private static readonly Regex UrlFinder = new Regex(@"ss://(?<base64>[A-Za-z0-9+-/=_]+)(?:#(?<tag>\S+))?", RegexOptions.IgnoreCase | RegexOptions.Compiled);
+        private static readonly Regex DetailsParser = new Regex(@"^((?<method>.+?):(?<password>.*)@(?<hostname>.+?):(?<port>\d+?))$", RegexOptions.IgnoreCase | RegexOptions.Compiled);
 
-        private static ProfileItem ResolveSSLegacy(string result)
+        private static ProfileItem? ResolveSSLegacy(string result)
         {
             var match = UrlFinder.Match(result);
             if (!match.Success)
@@ -627,7 +627,7 @@ namespace v2rayN.Handler
         private static readonly Regex StdVmessUserInfo = new Regex(
             @"^(?<network>[a-z]+)(\+(?<streamSecurity>[a-z]+))?:(?<id>[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12})$", RegexOptions.Compiled);
 
-        private static ProfileItem ResolveSocks(string result)
+        private static ProfileItem? ResolveSocks(string result)
         {
             ProfileItem profileItem = new ProfileItem
             {
@@ -675,7 +675,7 @@ namespace v2rayN.Handler
             return profileItem;
         }
 
-        private static ProfileItem ResolveSocksNew(string result)
+        private static ProfileItem? ResolveSocksNew(string result)
         {
             Uri parsedUrl;
             try
diff --git a/v2rayN/v2rayN/Handler/StatisticsHandler.cs b/v2rayN/v2rayN/Handler/StatisticsHandler.cs
index cb747f46..1421f239 100644
--- a/v2rayN/v2rayN/Handler/StatisticsHandler.cs
+++ b/v2rayN/v2rayN/Handler/StatisticsHandler.cs
@@ -13,7 +13,7 @@ namespace v2rayN.Handler
         private Channel channel_;
         private StatsService.StatsServiceClient client_;
         private bool exitFlag_;
-        private ServerStatItem _serverStatItem;
+        private ServerStatItem? _serverStatItem;
         private List<ServerStatItem> _lstServerStat;
         public List<ServerStatItem> ServerStat => _lstServerStat;
 
@@ -70,7 +70,7 @@ namespace v2rayN.Handler
                 {
                     if (Enable && channel_.State == ChannelState.Ready)
                     {
-                        QueryStatsResponse res = null;
+                        QueryStatsResponse? res = null;
                         try
                         {
                             res = client_.QueryStats(new QueryStatsRequest() { Pattern = "", Reset = true });
diff --git a/v2rayN/v2rayN/Handler/SysProxyHandle.cs b/v2rayN/v2rayN/Handler/SysProxyHandle.cs
index c0dd4f8d..1c979b8e 100644
--- a/v2rayN/v2rayN/Handler/SysProxyHandle.cs
+++ b/v2rayN/v2rayN/Handler/SysProxyHandle.cs
@@ -20,7 +20,7 @@ namespace v2rayN.Handler
         //  <proxy-server><CR-LF>
         //  <bypass-list><CR-LF>
         //  <pac-url>
-        private static SysproxyConfig _userSettings = null;
+        private static SysproxyConfig? _userSettings = null;
 
         enum RET_ERRORS : int
         {
@@ -174,8 +174,8 @@ namespace v2rayN.Handler
 
                     process.StartInfo.CreateNoWindow = true;
 
-                    StringBuilder output = new StringBuilder();
-                    StringBuilder error = new StringBuilder();
+                    StringBuilder output = new StringBuilder(1024);
+                    StringBuilder error = new StringBuilder(1024);
 
                     process.OutputDataReceived += (sender, e) =>
                     {
diff --git a/v2rayN/v2rayN/Handler/TunHandler.cs b/v2rayN/v2rayN/Handler/TunHandler.cs
index ef0e99ff..04c0075b 100644
--- a/v2rayN/v2rayN/Handler/TunHandler.cs
+++ b/v2rayN/v2rayN/Handler/TunHandler.cs
@@ -13,7 +13,7 @@ namespace v2rayN.Base
         private string _tunConfigName = "tunConfig.json";
         private static Config _config;
         private CoreInfo coreInfo;
-        private Process _process;
+        private Process? _process;
         private static int _socksPort;
         private static bool _needRestart = true;
         private static bool _isRunning = false;
diff --git a/v2rayN/v2rayN/Handler/UpdateHandle.cs b/v2rayN/v2rayN/Handler/UpdateHandle.cs
index a3ba3777..0172fe5e 100644
--- a/v2rayN/v2rayN/Handler/UpdateHandle.cs
+++ b/v2rayN/v2rayN/Handler/UpdateHandle.cs
@@ -35,51 +35,46 @@ namespace v2rayN.Handler
             _updateFunc = update;
             var url = string.Empty;
 
-            DownloadHandle downloadHandle = null;
-            if (downloadHandle == null)
+            DownloadHandle downloadHandle = new DownloadHandle();
+            downloadHandle.UpdateCompleted += (sender2, args) =>
             {
-                downloadHandle = new DownloadHandle();
-
-                downloadHandle.UpdateCompleted += (sender2, args) =>
+                if (args.Success)
                 {
-                    if (args.Success)
-                    {
-                        _updateFunc(false, ResUI.MsgDownloadV2rayCoreSuccessfully);
+                    _updateFunc(false, ResUI.MsgDownloadV2rayCoreSuccessfully);
 
-                        try
+                    try
+                    {
+                        string fileName = Utils.GetTempPath(Utils.GetDownloadFileName(url));
+                        fileName = Utils.UrlEncode(fileName);
+                        Process process = new Process
                         {
-                            string fileName = Utils.GetTempPath(Utils.GetDownloadFileName(url));
-                            fileName = Utils.UrlEncode(fileName);
-                            Process process = new Process
+                            StartInfo = new ProcessStartInfo
                             {
-                                StartInfo = new ProcessStartInfo
-                                {
-                                    FileName = "v2rayUpgrade.exe",
-                                    Arguments = $"\"{fileName}\"",
-                                    WorkingDirectory = Utils.StartupPath()
-                                }
-                            };
-                            process.Start();
-                            if (process.Id > 0)
-                            {
-                                _updateFunc(true, "");
+                                FileName = "v2rayUpgrade.exe",
+                                Arguments = $"\"{fileName}\"",
+                                WorkingDirectory = Utils.StartupPath()
                             }
-                        }
-                        catch (Exception ex)
+                        };
+                        process.Start();
+                        if (process.Id > 0)
                         {
-                            _updateFunc(false, ex.Message);
+                            _updateFunc(true, "");
                         }
                     }
-                    else
+                    catch (Exception ex)
                     {
-                        _updateFunc(false, args.Msg);
+                        _updateFunc(false, ex.Message);
                     }
-                };
-                downloadHandle.Error += (sender2, args) =>
+                }
+                else
                 {
-                    _updateFunc(false, args.GetException().Message);
-                };
-            }
+                    _updateFunc(false, args.Msg);
+                }
+            };
+            downloadHandle.Error += (sender2, args) =>
+            {
+                _updateFunc(false, args.GetException().Message);
+            };
             AbsoluteCompleted += (sender2, args) =>
             {
                 if (args.Success)
@@ -106,36 +101,32 @@ namespace v2rayN.Handler
             _updateFunc = update;
             var url = string.Empty;
 
-            DownloadHandle downloadHandle = null;
-            if (downloadHandle == null)
+            DownloadHandle downloadHandle = new DownloadHandle();
+            downloadHandle.UpdateCompleted += (sender2, args) =>
             {
-                downloadHandle = new DownloadHandle();
-                downloadHandle.UpdateCompleted += (sender2, args) =>
+                if (args.Success)
                 {
-                    if (args.Success)
-                    {
-                        _updateFunc(false, ResUI.MsgDownloadV2rayCoreSuccessfully);
-                        _updateFunc(false, ResUI.MsgUnpacking);
+                    _updateFunc(false, ResUI.MsgDownloadV2rayCoreSuccessfully);
+                    _updateFunc(false, ResUI.MsgUnpacking);
 
-                        try
-                        {
-                            _updateFunc(true, url);
-                        }
-                        catch (Exception ex)
-                        {
-                            _updateFunc(false, ex.Message);
-                        }
-                    }
-                    else
+                    try
                     {
-                        _updateFunc(false, args.Msg);
+                        _updateFunc(true, url);
                     }
-                };
-                downloadHandle.Error += (sender2, args) =>
+                    catch (Exception ex)
+                    {
+                        _updateFunc(false, ex.Message);
+                    }
+                }
+                else
                 {
-                    _updateFunc(true, args.GetException().Message);
-                };
-            }
+                    _updateFunc(false, args.Msg);
+                }
+            };
+            downloadHandle.Error += (sender2, args) =>
+            {
+                _updateFunc(true, args.GetException().Message);
+            };
 
             AbsoluteCompleted += (sender2, args) =>
             {
@@ -226,7 +217,7 @@ namespace v2rayN.Handler
                     else
                     {
                         _updateFunc(false, $"{hashCode}{ResUI.MsgGetSubscriptionSuccessfully}");
-                        if (result.Length < 99)
+                        if (result!.Length < 99)
                         {
                             _updateFunc(false, $"{hashCode}{result}");
                         }
@@ -262,49 +253,44 @@ namespace v2rayN.Handler
             _updateFunc = update;
             var url = string.Format(Global.geoUrl, geoName);
 
-            DownloadHandle downloadHandle = null;
-            if (downloadHandle == null)
+            DownloadHandle downloadHandle = new DownloadHandle();
+            downloadHandle.UpdateCompleted += (sender2, args) =>
             {
-                downloadHandle = new DownloadHandle();
-
-                downloadHandle.UpdateCompleted += (sender2, args) =>
+                if (args.Success)
                 {
-                    if (args.Success)
+                    _updateFunc(false, string.Format(ResUI.MsgDownloadGeoFileSuccessfully, geoName));
+
+                    try
                     {
-                        _updateFunc(false, string.Format(ResUI.MsgDownloadGeoFileSuccessfully, geoName));
-
-                        try
+                        string fileName = Utils.GetTempPath(Utils.GetDownloadFileName(url));
+                        if (File.Exists(fileName))
                         {
-                            string fileName = Utils.GetTempPath(Utils.GetDownloadFileName(url));
-                            if (File.Exists(fileName))
-                            {
-                                //Global.coreTypes.ForEach(it =>
-                                //{
-                                //    string targetPath = Utils.GetBinPath($"{geoName}.dat", (ECoreType)Enum.Parse(typeof(ECoreType), it));
-                                //    File.Copy(fileName, targetPath, true);
-                                //});
-                                string targetPath = Utils.GetBinPath($"{geoName}.dat");
-                                File.Copy(fileName, targetPath, true);
+                            //Global.coreTypes.ForEach(it =>
+                            //{
+                            //    string targetPath = Utils.GetBinPath($"{geoName}.dat", (ECoreType)Enum.Parse(typeof(ECoreType), it));
+                            //    File.Copy(fileName, targetPath, true);
+                            //});
+                            string targetPath = Utils.GetBinPath($"{geoName}.dat");
+                            File.Copy(fileName, targetPath, true);
 
-                                File.Delete(fileName);
-                                //_updateFunc(true, "");
-                            }
-                        }
-                        catch (Exception ex)
-                        {
-                            _updateFunc(false, ex.Message);
+                            File.Delete(fileName);
+                            //_updateFunc(true, "");
                         }
                     }
-                    else
+                    catch (Exception ex)
                     {
-                        _updateFunc(false, args.Msg);
+                        _updateFunc(false, ex.Message);
                     }
-                };
-                downloadHandle.Error += (sender2, args) =>
+                }
+                else
                 {
-                    _updateFunc(false, args.GetException().Message);
-                };
-            }
+                    _updateFunc(false, args.Msg);
+                }
+            };
+            downloadHandle.Error += (sender2, args) =>
+            {
+                _updateFunc(false, args.GetException().Message);
+            };
             askToDownload(downloadHandle, url, false);
 
         }
diff --git a/v2rayN/v2rayN/Tool/Utils.cs b/v2rayN/v2rayN/Tool/Utils.cs
index 43359be6..6f4e5e69 100644
--- a/v2rayN/v2rayN/Tool/Utils.cs
+++ b/v2rayN/v2rayN/Tool/Utils.cs
@@ -48,7 +48,8 @@ namespace v2rayN
             try
             {
                 Assembly assembly = Assembly.GetExecutingAssembly();
-                using Stream stream = assembly.GetManifestResourceStream(res);
+                using Stream? stream = assembly.GetManifestResourceStream(res);
+                ArgumentNullException.ThrowIfNull(stream);
                 using StreamReader reader = new(stream);
                 result = reader.ReadToEnd();
             }
@@ -90,7 +91,7 @@ namespace v2rayN
         /// <typeparam name="T"></typeparam>
         /// <param name="strJson"></param>
         /// <returns></returns>
-        public static T FromJson<T>(string strJson)
+        public static T? FromJson<T>(string strJson)
         {
             try
             {
@@ -98,8 +99,7 @@ namespace v2rayN
                 {
                     return default;
                 }
-                T obj = JsonConvert.DeserializeObject<T>(strJson);
-                return obj;
+                return JsonConvert.DeserializeObject<T>(strJson);
             }
             catch
             {
@@ -112,7 +112,7 @@ namespace v2rayN
         /// </summary>
         /// <param name="obj"></param>
         /// <returns></returns>
-        public static string ToJson(object obj, bool indented = true)
+        public static string ToJson(object? obj, bool indented = true)
         {
             string result = string.Empty;
             try
@@ -141,7 +141,7 @@ namespace v2rayN
         /// <param name="obj"></param>
         /// <param name="filePath"></param>
         /// <returns></returns>
-        public static int ToJsonFile(object obj, string filePath, bool nullValue = true)
+        public static int ToJsonFile(object? obj, string filePath, bool nullValue = true)
         {
             int result;
             try
@@ -168,7 +168,7 @@ namespace v2rayN
             return result;
         }
 
-        public static JObject ParseJson(string strJson)
+        public static JObject? ParseJson(string strJson)
         {
             try
             {
@@ -676,7 +676,7 @@ namespace v2rayN
             return Application.StartupPath;
         }
 
-        public static string RegReadValue(string path, string name, string def)
+        public static string? RegReadValue(string path, string name, string def)
         {
             RegistryKey? regKey = null;
             try
@@ -737,7 +737,7 @@ namespace v2rayN
         public static bool CheckForDotNetVersion(int release = 528040)
         {
             const string subkey = @"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\";
-            using RegistryKey ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(subkey);
+            using RegistryKey? ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(subkey);
             if (ndpKey != null && ndpKey.GetValue("Release") != null)
             {
                 return (int)ndpKey.GetValue("Release") >= release ? true : false;
@@ -908,7 +908,7 @@ namespace v2rayN
         /// 获取剪贴板数
         /// </summary>
         /// <returns></returns>
-        public static string GetClipboardData()
+        public static string? GetClipboardData()
         {
             string strData = string.Empty;
             try
@@ -995,7 +995,7 @@ namespace v2rayN
             return fileName;
         }
 
-        public static IPAddress GetDefaultGateway()
+        public static IPAddress? GetDefaultGateway()
         {
             return NetworkInterface
                 .GetAllNetworkInterfaces()
diff --git a/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs b/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs
index e8a687ad..9dd0ccb2 100644
--- a/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs
+++ b/v2rayN/v2rayN/ViewModels/MainWindowViewModel.cs
@@ -532,7 +532,7 @@ namespace v2rayN.ViewModels
         {
             _noticeHandler?.SendMessage(msg);
         }
-        private async void UpdateTaskHandler(bool success, string msg)
+        private void UpdateTaskHandler(bool success, string msg)
         {
             _noticeHandler?.SendMessage(msg);
             if (success)