diff --git a/docs/03-tutorials/02-hubs-browser/_shared/dotnet/data/endpoints.mdx b/docs/03-tutorials/02-hubs-browser/_shared/dotnet/data/endpoints.mdx
index e849b93..cf495f8 100644
--- a/docs/03-tutorials/02-hubs-browser/_shared/dotnet/data/endpoints.mdx
+++ b/docs/03-tutorials/02-hubs-browser/_shared/dotnet/data/endpoints.mdx
@@ -46,7 +46,7 @@ public class HubsController : ControllerBase
     }
 
     [HttpGet("{hub}/projects/{project}/contents")]
-    public async Task<ActionResult> ListItems(string hub, string project, [FromQuery] string folder_id)
+    public async Task<ActionResult> ListItems(string hub, string project, [FromQuery] string? folder_id)
     {
         var tokens = await AuthController.PrepareTokens(Request, Response, _aps);
         if (tokens == null)