how to solve DataTables warning: Invalid JSON response in codeigniter

Question

I'm having problems displaying data into a data table, but when I check in the console the data appears and the response is 200 . but i'm having trouble displaying it in view , i get a message that the response is invalid json

this my view

 <table id="tabel" class="table table-striped" cellspacing="0" width="100%">
     <thead>
       <tr>
         <th>No</th>
         <th>Name</th>
         <th>Deskripsi</th>
         <th>Lokasi</th>
       </tr>
     </thead>
     <tbody></tbody>
   </table>

    <script type="text/javascript">
   $(document).ready(function() {
     $('#tabel').DataTable({
       "processing": true,
       "serverSide": true,
       "order": [],
        "ajax": {
                "url": "<?php echo site_url('main/ajax_list')?>",
                "type": "POST",
            },
            "columnDefs": [
                { 
                    "targets": [ 0 ], 
                    "orderable": false,
                },
            ],
     });
   });
 </script>

in this my controller

public function ajax_list()
    {
        $list = $this->M_master->get_datatables();
        $data = array();
        $no = $_POST['start'];
        foreach ($list as $datas) {
            $no++;
            $row = array();
            $row[] = $no;
            $row[] = $datas->name;
            $row[] = $datas->description;
            $row[] = $datas->location;
 
            $data[] = $row;
        }
 
        $output = array(
                    "draw" => intval($_POST["draw"]),
                    "recordsTotal" => $this->M_master->count_all(),
                    "recordsFiltered" => $this->M_master->count_filtered(),
                    "data" => $data,
                );
        echo json_encode($output);
    }

and this my model

class M_master extends CI_Model {
    var $table = 'rumah';
    var $column = array('name','description','location');
    var $order = array('id' => 'desc');
 
    public function __construct()
    {
        parent::__construct();
        $this->load->database();
    }
 
    private function _get_datatables_query()
    {

        $this->db->from($this->table);
 
        $i = 0;
     
        foreach ($this->column_search as $item) 
        {
            if($_POST['search']['value'])
            {
                 
                if($i===0) 
                {
                    $this->db->group_start();
                    $this->db->like($item, $_POST['search']['value']);
                }
                else
                {
                    $this->db->or_like($item, $_POST['search']['value']);
                }
 
                if(count($this->column_search) - 1 == $i) 
                    $this->db->group_end(); 
            }
            $i++;
        }
         
        if(isset($_POST['order'])) 
        {
            $this->db->order_by($this->column_order[$_POST['order']['0']['column']], $_POST['order']['0']['dir']);
        } 
        else if(isset($this->order))
        {
            $order = $this->order;
            $this->db->order_by(key($order), $order[key($order)]);
        }
    }
 
    public function get_datatables()
    {
        $this->_get_datatables_query();
        if($_POST['length'] != -1)
        $this->db->limit($_POST['length'], $_POST['start']);
        $query = $this->db->get();
        return $query->result();
    }
 
    public function count_filtered()
    {
        $this->_get_datatables_query();
        $query = $this->db->get();
        return $query->num_rows();
    }
 
    public function count_all()
    {
        $this->db->from($this->table);
        return $this->db->count_all_results();
    }
 
}

and this response my console

where is the error? while my console managed to display the data