Bind.path constructor Null safety

Binds a route variable from RequestPath.variables to an ResourceController operation method argument.

Routes may have path variables, e.g., a route declared as follows has an optional path variable named 'id':

    router.route("/users/[:id]");

A operation method is invoked if it has exactly the same path bindings as the incoming request's path variables. For example, consider the above route and a controller with the following operation methods:

    class UserController extends ResourceController {
      @Operation.get()
      Future<Response> getUsers() async => Response.ok(getAllUsers());
      @Operation.get('id')
      Future<Response> getOneUser(@Bind.path("id") int id) async => Response.ok(getUser(id));
    }

If the request path is /users/1, /users/2, etc., getOneUser is invoked because the path variable id is present and matches the Bind.path argument. If no path variables are present, getUsers is invoked.