I had Error: Argument passed in must be a single String of 12 bytes or a string of 24 hex characters, How to fix it? i need a example code for sure

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this is my code, I've tried several references but I can't find a solution for my case. please help, i need some example for sure..

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app.post('/sendFriendRequest', function (request, result) {
  var accessToken = request.fields.accessToken;
  var _id = request.fields._id;

  database.collection('users').findOne(
    {
      accessToken: accessToken,
    },
    function (error, user) {
      if (user == null) {
        result.json({
          status: 'error',
          message: 'Pengguna telah keluar. Silahkan masuk kembali.',
        });
      } else {
        var me = user;
        database.collection('users').findOne(
          {
            _id: ObjectId(),
          },
          function (error, user) {
            if (user == null) {
              result.json({
                status: 'error',
                message: 'Pengguna tidak ditemukan.',
              });
            } else {
              database.collection('users').updateOne(
                {
                  _id: ObjectId(),
                },

this is part of my code