Collection Undefined on a Simple Migration about mongo-migrate HOT 3 CLOSED

'use strict';

module.exports = {

  up: function (db, next) {
    // TODO write your migration here
   var Activity = db.Collection('Activity');
   Activity.update({}, {$set: {"runtime" : {
                                                    "started" : false,
                                                    "startDate" : null,
                                                    "endDate" : null
                                                }
                                   }
                            }, 
                        false, true);
    next();
  },

  down: function (db, next) {
    // TODO write the statements to rollback your migration (if possible)
    var Activity = db.Collection('Activity');
   Activity.update({}, {$unset: {"runtime" : ""}}, false, true);
    next();
  }

};`