added condition for this.expire not defined

  // Save file in a key

  set(key, data, callback, skipExpire) {

    var now = new Date();

    var expireTime = skipExpire ? null : new Date(now.getTime() + this.expire * 1000);

    var expireTime = (skipExpire || this.expire === undefined) ? null : new Date(now.getTime() + this.expire * 1000);

    var taskKey = this.datastore.key([this.kind, key])

    var task = {