fix server null exception

MultiThreadTCPServer/Server.cs

@@ -27,7 +27,7 @@ namespace MultiThreadTCPServer
                     Console.WriteLine("Connected!");
 
                     Thread t = new Thread(new ParameterizedThreadStart(HandleClient));
-                    t.Start();
+                    t.Start(client);
                 }
             }
             catch (SocketException e)
@@ -37,7 +37,7 @@ namespace MultiThreadTCPServer
             }
         }
 
-        private void HandleClient(object? obj)
+        public void HandleClient(object obj)
         {
             TcpClient client = (TcpClient)obj;
             var stream = client.GetStream();