I'm currently building a project that deals with Discord users. For those who don't know, each Discord user has a unique Id, stored as `ulong`.

I am trying to route this Id to my page (currently looks like this)

```
@page "{UserId:ulong?}"
@model BotFrameworkInterface.Pages.Bot.UserDetailsModel
@{
    ViewData["Title"] = "UserDetails";
}

<h1>UserDetails</h1>

@foreach(var u in Model.SelectedUsers)
{
    <Partial name="_Summary" model="u"/>
}

```

but it breaks and gives me the following exception:

> 
> InvalidOperationException: The constraint reference 'ulong' could not
>  be resolved to a type. Register the constraint type with
>  'Microsoft.AspNetCore.Routing.RouteOptions.ConstraintMap'.
> 
> 
> 

is there any way I can pass in a `ulong` into my ASP.NET (core) page? (the partial view works fine, I checked it)