Support for the Ruby 2.4 series has ended. See here for reference.
# File rss/maker/atom.rb, line 85 def to_feed(feed, current) category = feed.class::Category.new set = setup_values(category) if set current.categories << category set_parent(category, current) setup_other_elements(feed) else raise NotSetError.new(self.class.not_set_name, not_set_required_variables) end end