Mongoose - causé par :: 11000 E11000 erreur de clé en double index?

Pourquoi j'obtiens cette erreur de doublons - Error creating new user: WriteError({"code":11000,"index":0,"errmsg":"insertDocument :: caused by :: 11000 E11000 duplicate key error index?

Tous les champs ne sont pas vides.

Schéma:

//Declare schema
var userSchema = new mongoose.Schema({
    username: {type: String, required: true, index: {unique: true}},
    password: {type: String, required: true},
    created_on: {type: Date, default: Date.now}
});

Post:

//Create - POST
//Create the first method of the API : POST used to create a new user.
router.post("/", function(req, res, next) {
    //Get values from POST request
    var username = req.body.username;
    var password = req.body.password;
    console.log(req.body); //{ username: 'tealou', password: 'test123' }

    //Create new user document
    User.create({
        username: username,
        password: password
    }, function(err, user) {
        console.log(user); //undefined
        if (err) {
            console.log("Error creating new user: " + err);
            res.send("Error creating new user.");
        } else {
            console.log("POST creating new user: " + username);
            res.json(user);
        }
    })
});

Erreur:

Erreur de création du nouvel utilisateur:
WriteError({"code":11000,"index":0,"errmsg":"insertDocument :: causé
par :: 11000 E11000 erreur de clé en double index: iotdb.utilisateurs.$name_1 dup
clé: { : null
}","op":{"username":"tealou","password":"$2a$10$7mPGND2FRuJDGnXaVTnkru2.xsGn2Ksf8veBKur4ouD9VUNj60RaC","_id":"5786020088245d33140d6f94","created_on":"2016-07-13T08:55:28.279 Z","__v":0}})

des idées?

OriginalL'auteur laukok | 2016-07-13