ASP.NET Core 2.2 Upgrade Routing from 2.1 to 2.2 - asp.net-core-2.2

Question

I am upgrading my application from ASP.NET Core 2.1 to 2.2. There is a change in the routing that I am having problems with. I have reviewed the following links as a source.
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/routing?view=aspnetcore-2.2
https://blogs.msdn.microsoft.com/webdev/2018/08/27/asp-net-core-2-2-0-preview1-endpoint-routing/
Here is my Core 2.1 code in Startup.cs
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
//Area Marketing
routes.MapRoute(name: "Marketing",
template: "Marketing/{controller}/{action}/{id?}");
//Area Media
routes.MapRoute(name: "Media",
template: "Media/{controller}/{action}/{id?}");
//Area Membership
routes.MapRoute(name: "Membership",
template: "Membership/{controller}/{action}/{id?}");
//Area Military
routes.MapRoute(name: "Military",
template: "Military/{controller}/{action}/{id?}");
//Area Process
routes.MapRoute(name: "Process",
template: "Process/{controller}/{action}/{id?}");
});
Here is my Core 2.2 code in Startup.cs that I have migrated.
//ASP.NET Core 2.2 Routes
var routes = new RouteBuilder(app);
//
//routes.DefaultHandler = new MvcRouteHandler(???);
//
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
//Area Marketing
routes.MapRoute(name: "Marketing",
template: "Marketing/{controller}/{action}/{id?}");
//Area Media
routes.MapRoute(name: "Media",
template: "Media/{controller}/{action}/{id?}");
//Area Membership
routes.MapRoute(name: "Membership",
template: "Membership/{controller}/{action}/{id?}");
//Area Military
routes.MapRoute(name: "Military",
template: "Military/{controller}/{action}/{id?}");
//Area Process
routes.MapRoute(name: "Process",
template: "Process/{controller}/{action}/{id?}");
app.UseRouter(routes.Build());
}
When I run the applicaiton I get the following error:
It looks like I need to create or setup a Handler for this. What would my Handler code look like as there are not any examples or tutorials that I can find.