validateMaxAgeSeconds(seconds) {
        if (!seconds) {
            return undefined;
        }
        if (!Array.isArray(seconds) || seconds.length !== 1) {
            return errors.MalformedXML;
        }
        if (seconds[0] === '') {
            return undefined;
        }
        const parsedValue = parseInt(seconds[0], 10);
        const errMsg = `MaxAgeSeconds "${seconds[0]}" is not a valid value.`;
        if (Number.isNaN(parsedValue) || parsedValue < 0) {
            return errorInstances.MalformedXML.customizeDescription(errMsg);
        }
        return parsedValue;
    }
_validator.validateMaxAgeSeconds - check value of optional MaxAgeSeconds
@param {string[]} seconds - array containing number string
@return {(Error|parsedValue|undefined)} - Arsenal error on failure, parsed
  value if valid, undefined if MaxAgeSeconds does not exist