Trying to get property of non-object

Hi all, 
I want to make a table with the members list of my website, but i have Trying to get property of non-object as error.

Here is my controller:

Code:

       public function memberslist(){
               $template = array(
                       'table_open'            => '<table class="table table-hover table-responsive" style= "background-color:white;">',
                       'tbody_open'            => '<tbody class="table-striped">',
               );
                                $this->table->set_template($template);
               $tableau = array($this->admin_model->memberslist());
               $data['tableau'] = $this->table->generate($tableau);
               $data['title'] = 'Liste des membres';
               $this->load->view('admin/memberslist', $data);
       }

Here is my model:

Code:

     public function memberslist(){
         $this->db->select('*');
         $this->db->from('users');
         $this->db->order_by('username', 'ASC');
         $query = $this->db->get();
         $userlist = array();
         foreach ($query->result_array() as $row)
         {
           $userlist .= array($row->id, $row->username, $row->vip, $row->administrator);
         }
         return $userslist;        
     }

I want make a table in my table with all members list, am i wrong?