datatables.yajrabox laravel 5.4 error

using laravel 5.4 I get an error when I try to run the index view. Checking in firebug, I get this:

ErrorException in Datatables.php line 57: Invalid argument supplied for foreach()

My routes:

Route::get('promotions.data', 'PromotionController@getPromotions')->name('promotions.data');
Route::resource('promotions', 'PromotionController');

My ajax call:

$('#promotionsTbl').DataTable({
                processing: true,
                serverSide: true,
                ajax: '{!! url('promotions.data') !!}',
                columns: [
                    { data: 'id', name: 'id' },
                    { data: 'name', name: 'name' },
                    { data: 'from_date', name: 'from_date' },
                    { data: 'to_date', name: 'to_date' }
                ]
            });

My Controller:

public function getPromotions()
   {
       return Datatables::of(Promotion::query())->make(true);
   }

Can anyone please help?

via Chebli Mohamed