nodejs model updateOne does NOT give same result

Trying to update a document in mongodb using the following method :

module.exports.addAcc = function(id , acc, callback) {
    let strAcc  = escape(JSON.stringify(acc, null, 4));

    let pushAcc =  '{'+ ' $push :'+ '{ "pf.acc" : '  +strAcc + '}}' ;
    let query = '{ "userid": ' + id + '}'; 

    console.log('udpate <<',query,',' ,pushAcc, '>>');   <=====

    Api.updateOne(query, pushAcc, {upsert: false},  callback);

};

it does give the following result :

{
"ok": 0,
"n": 0,
"nModified": 0
}

And When I catch what's in the console.log line and replace it in the Api.updateOne line, like this:

Api.updateOne({ "userid": 1197} , { $push :{ "pf.acc" : {"accid":1496998168,"accbr":65875}}}, {upsert: false}, callback);

it WORKS !!

{
"n": 1,
"nModified": 1,
"ok": 1
}

any idea why is that ?

/KOul

via K Oul