co-monk yield call not working on function generator inside a class

[wmehanna]

I'm getting undefined ouput when calling for the returned value comming from the yield call.
It worked with co library.

here's my code :

"use strict";

 var monk = require("monk");
 var wrap = require("co-monk");
 var db = monk("localhost/test");
 var users = wrap(db.get("users"));

 class User {

    constructor(user) {
        if (typeof user == "object") {

            var findUser = this.findOne(user.id);
            findUser.next();
            findUser.next();

            if(findUser != null){
                this._user = user;
            }

        }
        else {
            console.error("user parameter is not an oject");
            return false;
        }
    }

    *findOne(id) {

        var userData = yield users.findOne({_id: id});

        console.log(userData); // Getting undefined

        this._user = userData;

    };
}