Why does the node.js error occur again?

Question

Node.js

here is the code

var  mongoose = require("./libs/mongoose");
var User = require("./models/user").User;
var asyng = require('async');

asyng.series([
    open,
    dropDatabase,
    createUsers,
    close
],function (err,results) {
    if(err) throw err;
    console.log(arguments);
});

function open(callback) {
    mongoose.connection.on('open',callback);
}

function dropDatabase(callback) {
    var db = mongoose.connection.db;
    db.dropDatabase(callback);
}
function createUsers(callback) {
    asyng.parallel([
        function (callback) {
            var vasya = new User({username:'Вася',password: 'supervasay'});
            vasya.save(function(err){
                callback(err,vasya);
            })
        },
        function (callback) {
            var petya = new User({username:'Петя',password: 'superpetya'});
            petya.save(function(err){
                callback(err,petya);
            })
        },
        function (callback) {
            var admin = new User({username:'admin',password: 'superadmin'});
            admin.save(function(err){
                callback(err,admin);
            })
        }],callback);


}
function close(callback) {
    mongoose.disconnect(callback);
}

gives such an error

{ '0': null,
  '1': [ undefined, true, [ [Object], [Object], [Object] ], undefined ] }

if I change it

function dropDatabase(err, callback) {
     if(err) throw err;
    var db = mongoose.connection.db;
    db.dropDatabase(callback);
}

getting like this

undefined

/var/www/html/chatnode/node_modules/mongoose/node_modules/mongodb/lib/server.js:309
      process.nextTick(function() { throw err; })
                                    ^
function () {
        var args = arguments,
            index = -1,
            length = nativeMax(args.length - start, 0),
            array = Array(length);

        while (++index < length) {
          array[index] = args[start + index];
        }
        switch (start) {
          case 0: return func.call(this, array);
          case 1: return func.call(this, args[0], array);
          case 2: return func.call(this, args[0], args[1], array);
        }
        var otherArgs = Array(start + 1);
        index = -1;
        while (++index < start) {
          otherArgs[index] = args[index];
        }
        otherArgs[start] = array;
        return apply(func, this, otherArgs);
      }

what am I doing wrong

Answer 1

gives such an error

This is not an error, but the correct operation of the call console.log(arguments);. The fact that the first argument is null just means that there is no error.

if I change it

The above code is identical to what is already in the example. What is changing?