Laravel 5.1 and illuminate html FORM

I have a problem with multiple select in laravel using illuminate html, I want to pre-select items, it works when I put them manuelly with an array like this :

{!! Form::select('tags_list[]', $tags, [2, 3], ['class' => 'form-control', 'multiple' => true]) !!}

But when I use a model to put the list, like this :

{!! Form::select('tags_list[]', $tags, $post->tags_list, ['class' => 'form-control', 'multiple' => true]) !!}

It doesn't work and I checked the list is returned correctly, here is the result of :

dd($post->tags_list);

Collection {#273 ▼
  #items: array:2 [▼
    0 => 1
    1 => 2
  ]
}

And here is the method that return the tags_list

public function getTagsListAttribute()
    {
        return $this->tags->lists('id');
    }

I am new in Laravel framework, can anyone help me with this issue, thanks in advance

via Chebli Mohamed