At the moment, it's hard to use our strongly-typed overloads strategy to generate code that correctly handles two route handlers with the same parameters but differing nullability:

app.MapPost("/foo", (Todo todo) => ...);
app.MapPost("/bar", (Todo? todo) => ...);

We might consider generating two different strongly-typed overloads, one with the nullability annotations and one without:

MapPost(System.Action<Todo>);
MapPost(System.Action<Todo?>);

But overload resolution is not able to discern between the two delegate signatures and treats them as ambiguous overloads.

We can also emit only the overload that expects an NRT:

MapPost(System.Action<Todo?>);

But that presents a nullability warning to users (CS8622) when passing an overload to the delegate that does not expect an NRT.