def fetched(key)
      value = self[key]
      return unless value

      # if value =~ /^not_found/
      #   value.match(/\d{4}-\d{2}-\d{2}/).to_s
      # else
      doc = Nokogiri::XML value
      doc.at("/bibitem/fetched")&.text
      # end
    end
def fetched(key)
      value = self[key]
      return unless value

      # if value =~ /^not_found/
      #   value.match(/\d{4}-\d{2}-\d{2}/).to_s
      # else
      doc = Nokogiri::XML value
      doc.at("/bibitem/fetched")&.text
      # end
    end
Return fetched date
 @param key [String]
 @return [String]