$row is only the number not a object

This is my program:

    $crud = new GroceryCrud();

    $crud->setLanguage('Spanish');

    $crud->setTheme('bootstrap-v4');
    $crud->setSubject('Mesas');
    $crud->setTable('Mesa');
    $crud->columns(['NMesa', 'Capacidad', 'Descripcion']);
  
    $crud->setActionButton('Listado', 'el el-file', function ($row) {
        return '/informe_management?id=3&format=excel&data=' . $row->NMesa;
    }, true);

    $output = $crud->render();

Why $row->NMesa is null at de view?

…/informe_management?id=3&format=excel&data=