diff --git a/src/FubarDev.FtpServer.Abstractions/Localization/EmptyLocalizationCatalog.cs b/src/FubarDev.FtpServer.Abstractions/Localization/EmptyLocalizationCatalog.cs
index 52293513..1a7b26dc 100644
--- a/src/FubarDev.FtpServer.Abstractions/Localization/EmptyLocalizationCatalog.cs
+++ b/src/FubarDev.FtpServer.Abstractions/Localization/EmptyLocalizationCatalog.cs
@@ -26,6 +26,6 @@ public EmptyLocalizationCatalog(CultureInfo cultureInfo)
 
         public virtual string GetString(string text) => text;
 
-        public virtual string GetString(string text, params object[] args) => string.Format(FormatProvider, text, args);
+        public virtual string GetString(string text, params object?[] args) => string.Format(FormatProvider, text, args);
     }
 }
diff --git a/src/FubarDev.FtpServer.Abstractions/Localization/ILocalizationCatalog.cs b/src/FubarDev.FtpServer.Abstractions/Localization/ILocalizationCatalog.cs
index 668fd41f..4cf2a1b6 100644
--- a/src/FubarDev.FtpServer.Abstractions/Localization/ILocalizationCatalog.cs
+++ b/src/FubarDev.FtpServer.Abstractions/Localization/ILocalizationCatalog.cs
@@ -15,6 +15,6 @@ public interface ILocalizationCatalog
         /// <param name="text">The text to be translated.</param>
         /// <param name="args">The format arguments.</param>
         /// <returns>The translated text.</returns>
-        string GetString(string text, params object[] args);
+        string GetString(string text, params object?[] args);
     }
 }
diff --git a/src/FubarDev.FtpServer/FtpConnection.cs b/src/FubarDev.FtpServer/FtpConnection.cs
index d86f6ac4..4f7a0fbb 100644
--- a/src/FubarDev.FtpServer/FtpConnection.cs
+++ b/src/FubarDev.FtpServer/FtpConnection.cs
@@ -115,7 +115,7 @@ public sealed class FtpConnection
         private readonly FtpConnectionKeepAlive _keepAlive;
 #pragma warning restore 612
 
-        private readonly IAuthorizationInformationFeature _authorizationInformationFeature;
+        private readonly IAuthorizationInformationFeature? _authorizationInformationFeature;
 
         private bool _connectionClosing;
 
@@ -383,8 +383,8 @@ await _serviceControl.WaitAsync(CancellationToken.None)
                         return;
                     }
 
-                    var currentUser = _authorizationInformationFeature.FtpUser;
-                    var membershipProvider = _authorizationInformationFeature.MembershipProvider;
+                    var currentUser = _authorizationInformationFeature?.FtpUser;
+                    var membershipProvider = _authorizationInformationFeature?.MembershipProvider;
                     if (currentUser != null
                         && membershipProvider is IMembershipProviderAsync membershipProviderAsync)
                     {
diff --git a/src/FubarDev.FtpServer/FtpServer.cs b/src/FubarDev.FtpServer/FtpServer.cs
index 8f654653..13d7a2bf 100644
--- a/src/FubarDev.FtpServer/FtpServer.cs
+++ b/src/FubarDev.FtpServer/FtpServer.cs
@@ -298,7 +298,7 @@ private async Task AddClientAsync(TcpClient client)
                 // Remember connection
                 if (!_connections.TryAdd(connection, new FtpConnectionInfo(scope)))
                 {
-                    _log.LogCritical("A new scope was created, but the connection couldn't be added to the list");
+                    _log?.LogCritical("A new scope was created, but the connection couldn't be added to the list");
                     client.Dispose();
                     scope.Dispose();
                     return;
diff --git a/src/FubarDev.FtpServer/ServiceCollectionExtensions.cs b/src/FubarDev.FtpServer/ServiceCollectionExtensions.cs
index 320cc587..f4477992 100644
--- a/src/FubarDev.FtpServer/ServiceCollectionExtensions.cs
+++ b/src/FubarDev.FtpServer/ServiceCollectionExtensions.cs
@@ -78,7 +78,7 @@ public static IServiceCollection AddFtpServer(
             services.AddScoped<IFeatureInfoProvider, DefaultFeatureInfoProvider>();
 
             services.AddScoped<TcpSocketClientAccessor>();
-            services.AddScoped(sp => sp.GetRequiredService<TcpSocketClientAccessor>().TcpSocketClient);
+            services.AddScoped(sp => sp.GetRequiredService<TcpSocketClientAccessor>().TcpSocketClient ?? throw new NullReferenceException("TCP socket client null"));
 
             services.AddScoped<IFtpConnection, FtpConnection>();
             services.AddScoped<IFtpLoginStateMachine, FtpLoginStateMachine>();