L5 Event and model serialize

I want to do some actions with uploaded file (like resize, backup to S3, .... ) In my controller. After a file was uploaded, a infomation of that file will be written into database through Upload model.

I call a event inside Upload model like this

class Upload  extends Model  {

public static function boot()
    {
        parent::boot();

        Upload::created(function($upload){
            event (new NewFileUploaded($upload));
        });
    }
}

Here is my event class:

<?php namespace Quiz\Events;

use Quiz\Events\Event;
use Illuminate\Queue\SerializesModels;
use Quiz\Models\Upload;

class NewFileUploaded extends Event {

    use SerializesModels;
    /**
     * @var Upload
     */
    public $upload;

    /**
     * Create a new event instance.
     *
     * @param Upload $upload
     * @return \Quiz\Events\NewFileUploaded
     */
    public function __construct(Upload $upload)
    {
        $this->upload = $upload;
    }

}

My Event handler :

<?php namespace Quiz\Handlers\Events;

use Illuminate\Queue\InteractsWithQueue;
use Illuminate\Contracts\Queue\ShouldBeQueued;
use Quiz\lib\Repositories\Upload\UploadRepository as Upload;

class RotateImage implements ShouldBeQueued {

    /**
     * Handle the event.
     *
     * @param  NewFileUploaded  $event
     * @return void
     */
    public function handle(NewFileUploaded $event)
    {
        $upload = $event->upload;
        dd($upload);
    }
}

And all I got is an instance of ModelIdentifier class with the correct model name and id but not the model itself.

Where am I doing wrong?