Expression body methods are evil

Creating a new controller with default action in ASP.NET can be easy. Let's take a look at some hastily written code:

public class FailController : Controller
{
  public void Index() => View();
}

Opening localhost:5000/fail yields blank page. Huh? Let's try localhost:5000/fail/index.

Still nothing...

Before madness strikes in notice that the action doesn't return anything. Let's fix that:

public class FailController : Controller
{
  public ActionResult Index() => View();
}

Now everything works and we can resume coding.