diff --git a/csharp/App/Backend/Controller.cs b/csharp/App/Backend/Controller.cs
index ca7deabb2..519684547 100644
--- a/csharp/App/Backend/Controller.cs
+++ b/csharp/App/Backend/Controller.cs
@@ -14,7 +14,7 @@ using Token = String;
 public class Controller : ControllerBase  
 {
     [HttpPost(nameof(Login))]
-    public ActionResult<Session> Login(String username, String password)
+    public ActionResult<Session> Login(String username, String? password)
     {
         var user = Db.GetUserByName(username);