How to show error message when handleRoute call fails?

[lrbridge]

In the Bike Share example and on the error test page if the ReactServerAgent calls fail then the associated RootElements aren't displayed.

I want to show an error to the user instead of not displaying the section. How would I do that?

(I know I could return a promise instead of calling next(), but I still want to have async calls and have the top of the page rendered before the RootElement when sections, so it seems like returning the promise isn't the right approach)