Support for the Ruby 2.4 series has ended. See here for reference.
 
               # File rss/maker/atom.rb, line 129
def to_feed(feed, current)
  generator = current.class::Generator.new
  if setup_values(generator)
    current.generator = generator
    set_parent(generator, current)
    setup_other_elements(feed)
  elsif variable_is_set?
    raise NotSetError.new(self.class.not_set_name,
                          not_set_required_variables)
  end
end