"Banned" OA Workaround account results in generic 500 error

Ideally it should redirect to the welcome page with a login-specific error message in the flash.

Sentry Issue: GALILEO-SEARCH-CG

ActionController::ActionControllerError: Cannot redirect to nil! (ActionController::ActionControllerError)
  app/controllers/sessions_controller.rb:55:in `new'
    redirect_to destination
...
(90 additional frame(s) were not displayed)