1. rails db:setup
2. create a conference with only acronym and title
3. add a day
4. Click Events -> Add Event. Supply a title and click "Create Event"
5. "edit people" - add yourself as a submitter
6. Click "Home"
7. The action now (wronlgy?) contains a "Participate" button.
8. Click "Participate", you get AbstractController::DoubleRenderError in Cfp::WelcomeController#show

Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like "redirect_to(...) and return".