static getExpirationTime(body = {}) {
    var hasExpirationTime = Object.prototype.hasOwnProperty.call(body, 'expiration_time');
    if (!hasExpirationTime) {
      return;
    }
    var expirationTimeParam = body['expiration_time'];
    var expirationTime;
    if (typeof expirationTimeParam === 'number') {
      expirationTime = new Date(expirationTimeParam * 1000);
    } else if (typeof expirationTimeParam === 'string') {
      expirationTime = new Date(expirationTimeParam);
    } else {
      throw new Parse.Error(
        Parse.Error.PUSH_MISCONFIGURED,
        body['expiration_time'] + ' is not valid time.'
      );
    }
    // Check expirationTime is valid or not, if it is not valid, expirationTime is NaN
    if (!isFinite(expirationTime)) {
      throw new Parse.Error(
        Parse.Error.PUSH_MISCONFIGURED,
        body['expiration_time'] + ' is not valid time.'
      );
    }
    return expirationTime.valueOf();
  }
Get expiration time from the request body.
@param {Object} request A request object
@returns {Number|undefined} The expiration time if it exists in the request