def stringify(hash)
      {}.tap do |h|
        hash.each { |key, value| h[key.to_s] = map_value_string(value) }
      end
    end
def stringify(hash)
      {}.tap do |h|
        hash.each { |key, value| h[key.to_s] = map_value_string(value) }
      end
    end
This method is called to convert all the keys of a hash into strings to allow consistent usage of hashes within your Ruby application.