Express не может прочитать регистрацию пользователя JSON

Question

Я работаю над своим первым приложением Express, и по какой-то причине Express / Mongo не может понять мой POST-запрос Postman при тестировании моей функции регистрации. Я получаю сообщение BulkWriteError, в котором утверждается, что имя пользователя не передано, а имя пользователя "null" уже занято. Я не знаю, что еще сказать о ситуации, но мне нужно добавить больше текста, чтобы можно было задать вопрос.

Users.js

// Register
router.post('/register', function (req, res, next) {
    let username = req.body.username;
    let email = req.body.email;
    let password1 = req.body.password1;
    let password2 = req.body.password2;

    // Check
    req.checkBody('username', "Username Is Required").notEmpty();
    req.checkBody('email', "Invalid Email Adress").isEmail();
    req.checkBody('password1', 'Password is required').notEmpty();
    req.checkBody('password2', 'Passwords do not match').equals(req.body.password1);

    let errors = req.validationErrors();

    if(errors) {
        console.log(errors);
    } else {
            MongoClient.connect(url, function(err, db) {
                if (err) throw err;

                let dbo = db.db('freeva');
                dbo.collection('users').find({username: username}, function (err, match) {
                    if (err) throw err;
                    if (match.username == username) {
                        console.log('Username Taken');
                        db.close();
                    }
                });
                dbo.collection('users').find({email: email}, function (err, match) {
                    if (err) throw err;
                    if (match.email == email) {
                        console.log('Email Taken');
                        db.close();
                    }
                });
            });

            let newUser =  new User ({
                username : username,
                email : email,
                password : password1,
                Following : [],
                FollowingCount : 0,
                Followers : [],
                FollowerCount: 0,
                TextPosts : [],
                Videos : [],
                Views: 0,
                EXP: 0,
                Featured: true
            });

            User.addUser(newUser, function (err) {
                if(err) {
                    console.log(err);
                } else {
                    console.log("Registration Successful");
                }
            });

            res.redirect('/users/login');
    }
});

user.js

module.exports.addUser = function(newUser, callback){
    bcrypt.genSalt(10, (err, salt) => {
        bcrypt.hash(newUser.password, salt, (err, hash) => {
            if(err) throw err;
            newUser.password = hash;
            newUser.save(callback);
        });
    });
};

РЕДАКТИРОВАТЬ: Консоль

// Console.log(req.body);
enter code here
{ email: 'test@gmail.com',
  username: 'Test',
  password1: 'testpass',
  password2: 'testpass' }
// If (err) throw err; (Error is from newUser.save in addUser function)
    { BulkWriteError: E11000 duplicate key error collection: freeva.users index: Username_1 dup key: { : null }
        at /Users/willhamilton/Desktop/freeva/node_modules/mongodb/lib/bulk/unordered.js:535:15
        at handleCallback (/Users/willhamilton/Desktop/freeva/node_modules/mongodb/lib/utils.js:128:55)
        at resultHandler (/Users/willhamilton/Desktop/freeva/node_modules/mongodb/lib/bulk/unordered.js:456:5)
        at /Users/willhamilton/Desktop/freeva/node_modules/mongodb/node_modules/mongodb-core/lib/connection/pool.js:544:18
        at process._tickCallback (internal/process/next_tick.js:176:11)
      name: 'BulkWriteError',
      message: 'E11000 duplicate key error collection: freeva.users index: Username_1 dup key: { : null }',
      driver: true,
      code: 11000,
      index: 0,
      errmsg: 'E11000 duplicate key error collection: freeva.users index: Username_1 dup key: { : null }',
      getOperation: [Function],
      toJSON: [Function],
      toString: [Function],
      result: 
       BulkWriteResult {
         ok: [Getter],
         nInserted: [Getter],
         nUpserted: [Getter],
         nMatched: [Getter],
         nModified: [Getter],
         nRemoved: [Getter],
         getInsertedIds: [Function],
         getUpsertedIds: [Function],
         getUpsertedIdAt: [Function],
         getRawResponse: [Function],
         hasWriteErrors: [Function],
         getWriteErrorCount: [Function],
         getWriteErrorAt: [Function],
         getWriteErrors: [Function],
         getLastOp: [Function],
         getWriteConcernError: [Function],
         toJSON: [Function],
         toString: [Function],
         isOk: [Function] } }