trying to use findAndModify from node.js to mongo: problem: no record inserted, null returned

mongo shell

// no such record insert

> use test
switched to db test
> show collections
system.indexes
test
> db.test.find()
{ "_id" : ObjectId("533d5ec091d39080c18ec8ba"), "_accountId" : "100000057408993" }
> 

output.txt

users.js: addUser: mongo example
'addUser: returns: null'

users.js

exports.addUser = function(req, res) {
    console.log("users.js: addUser: mongo example");
  var MongoClient = require('mongodb').MongoClient
    , format = require('util').format;    

  MongoClient.connect('mongodb://127.0.0.1:27017/test', function(err, db) {
    if(err) throw err;
    db.collection('test').findAndModify({hello: 'world'}, [['_id','asc']], {$set: {hi: 'there'}}, {}, function(err, object) {
      if (err) console.warn(err.message);
      else console.dir("addUser: returns: " + object);  // undefined if no matching object exists.
    });
  });
};