Rails 5 includes view helpers into controllers, so that they're available for Action Cable to publish messages from the controller. Rails 4 doesn't include helpers by default. The PushType CMS that I've been working with is Rails 4 and 5 compatible, and this was the first bug I ran into for Rails 4 support. It made the assumption that the helpers will be available. To fix, I had to include them into the needed class manually as part of my initialization script.