I´m trying to implement a DirectoryNamer, but unfortunately this results in an error message and I don´t know what to do next.

The Controller (excerpt):

```
if ($form->isSubmitted() && $form->isValid()) {

        $em = $this->getDoctrine()->getManager();
        $em->persist($image);
        $em->flush();
        //...
}

```

The DirectoryNamer Service Class:

```
use Vich\UploaderBundle\Naming\DirectoryNamerInterface;

class ArtistDirectoryNamer implements DirectoryNamerInterface
{
    public function directoryName($image, PropertyMapping $mapping) {   
        return $image->getArtist()->getId();
    }
}

```

The VichUploader Configuration:

```
vich_uploader:
db_driver: orm
mappings:
    upload_artists:
        uri_prefix:         /upload/artists
        upload_destination: %kernel.root_dir%/../web/upload/artists
        directory_namer:    macms_admin.artist_directory_namer
        namer:              vich_uploader.namer_uniqid
        inject_on_load:     false
        delete_on_update:   true
        delete_on_remove:   true

```

... and the reulting Error Message:

> 
> Compile Error: Declaration of ArtistDirectoryNamer::directoryName() must be compatible with Vich\UploaderBundle\Naming\DirectoryNamerInterface::directoryName($object, Vich\UploaderBundle\Mapping\PropertyMapping $mapping) 
> 
> 
> 

What´s wrong with my code? Until I´ve implemented the DirectoryNamer, the upload worked fine and the files have been stored in '/upload/artists'.

Any hints? Thanks in advance!