Delete File error

hi guys i am trying to delete the file while delete the product from the database but it show me errero and i didn't found any solution

    public function supprod($id,Request $request)
    {
      $produits=Produit::find($id);
      $produits->delete();
      $filename=(string)$document->nom;
      Storage::disk('fichier')->delete($filename);
      return redirect()->back();
    }

Image of the problem