mongoose/mongoDB/NodeJS multiple doc populate query

query.js

var notifyconfigs = [
    {path: 'notify_options_fk_key.buy_opt_container', model: 'BuyKeywordsOption'},
    {path: 'notify_options_fk_key.ask_opt_container', model: 'AskKeywordsOption'},
    {path: 'notify_options_fk_key.bid_opt_container', model: 'BidKeywordsOption'}
  ];

  if(req.params && req.params.id) {
        Usr
          .findById(req.params.id)
          .populate('notify_options_fk_key')
          .exec(function(err, user){
            if (!user) {
              helpers.sendJsonResponse(res, 404, {
                "message": "id not found"
              });
              return;
            } else if (err) {
              helpers.sendJsonResponse(res, 404, err);
              return;
            }

            Usr
                     .populate(user, notifyconfigs, function(err, result){
                       if (err) return helpers.sendJsonResponse(res, 404, err);
                       helpers.sendJsonResponse(res, 200, result);
                     });
          });
  } else {
    helpers.sendJsonResponse(res, 404, {
      "message": "No id in request"
    });
  }