How to use Capistrano v3 without multistage?

In the upgrade guide from v2, it says:

… you will have config/deploy/production.rb and config/deploy/staging.rb right after capifying. If you need only one stage, remove these files and declare stage (for example production) and servers in config/deploy.rb.

However, it doesn't show any specific example of how this should be configured. I'm getting an error "Stage not set, please call something such as cap production deploy, where production is a stage you have defined.", and if I add set :stage, :production, then I get:

TypeError: no implicit conversion of nil into String (TypeError)

        Pathname.new(deploy_to)
                     ^^^^^^^^^