Using `unless` doesn't have a big impact, so for this idiom, I don't really care if we follow the guidelines.  I've just been pointing out variations from idioms on the pull requests I've been reviewing for style and clarity.  Some idioms, like most one-liners with the suffixed `if` or `unless` I actually find detrimental to debugging with the worst being the trailing `rescue nil` as it has actually bitten us before for hiding bugs or not behaving as intended by the original author.