Bagaimana cara mengatasi error seperti ini?

A PHP Error was encountered

Severity: Notice

Message: Undefined property: Welcome::$model_barang

Filename: controllers/Welcome.php

Line Number: 23

Backtrace:

File: /home/vol18_2/epizy.com/epiz_28896231/htdocs/application/controllers/Welcome.php

Line: 23

Function: _error_handler

File: /home/vol18_2/epizy.com/epiz_28896231/htdocs/index.php

Line: 315

Function: require_once

An uncaught Exception was encountered

Type: Error

Message: Call to a member function tampil_data() on null

Filename: /home/vol18_2/epizy.com/epiz_28896231/htdocs/application/controllers/Welcome.php

Line Number: 23

Backtrace:

File: /home/vol18_2/epizy.com/epiz_28896231/htdocs/index.php

Line: 315

Function: require_once

INI UNTUK WELCOME.PHP

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Welcome extends CI_Controller {

    /**
     * Index Page for this controller.
     *
     * Maps to the following URL
     *      http://example.com/index.php/welcome
     *  - or -
     *      http://example.com/index.php/welcome/index
     *  - or -
     * Since this controller is set as the default controller in
     * config/routes.php, it's displayed at http://example.com/
     *
     * So any other public methods not prefixed with an underscore will
     * map to /index.php/welcome/<method_name>
     * @see https://codeigniter.com/user_guide/general/urls.html
     */
    public function index()
    {
        $data['barang'] = $this->model_barang->tampil_data()->result();
        $this->load->view('templates/header');
        $this->load->view('templates/sidebar');
        $this->load->view('dashboard',$data);
        $this->load->view('templates/footer');
    }
}

LALU INI KODING UNTUK MODEL_BARANG.PHP

<?php

class Model_barang extends CI_Model{
    public function tampil_data(){
        return $this->db->get('tb_barang');
    }
    public function tambah_barang($data,$table){
        $this->db->insert($table,$data);
    }
    public function edit_barang($where,$table){
        return $this->db->get_where($table,$where);
    }
    public function update_data($where,$data,$table)
    {
        $this->db->where($where);
        $this->db->update($table,$data);
    }
    public function hapus_data($where,$table){
        $this->db->where($where);
        $this->db->delete($table);
    }

    public function find($id)
    {
        $result =$this->db-> where('id_brg',$id)
                          -> limit(1)
                          -> get('tb_barang');
    if($result->num_rows()> 0){
        return $result->row();
    }else{
        return array();

        }

    }

    public function detail_brg($id_brg)
    {
        $result = $this->db->where('id_brg',$id_brg)->get('tb_barang');
        if($result->num_rows() >0){
            return $result->result();
        }else{
            return false;
        }
    }

}