Rendering of 404 not found JSON view not working

When setting json.override_notfound to true I didn't get a JSON response. 

After some research I found the following solution: 

The render method should return the rendered content according to the Slim documentation on: http://docs.slimframework.com/#Custom-Views

This fixed it for me, let me know if it breaks something else :)

Thanks for sharing this project. It really helped me getting started on my own REST API.