Symfony 3 - 不明白我的请求值为空的原因

I have checkboxes in my twig file depending on the users I want to delete. Then I have a button that refers to an action of the controller that is supposed to recover through the Request list of checked checkboxes. Only, each time, the list is null.

<th><a href="{{path('user_delete_masse')}}" type="submit" class="btn btn-danger"><span class="glyphicon glyphicon-remove"></span> Supprimer plusieurs utilisateurs </a></th>

//...
{% for ....%}

<td><input type="checkbox" name="usersSuppr[]" value={{unUser.username}} /></td>
{% endfor %}

controler :

/**
     * Suppression de plusieurs utilisateurs en même temps
     * 
     * @Route("/delete/masse", name="user_delete_masse")
     * @Method("GET")
     */
    public function deleteMasseAction(Request $request)
    {
        dump('delete masse');
        $em = $this->getDoctrine()->getManager(); //Récupération du manager

        $listeUsernames=$request->get('usersSuppr');
        dump($listeUsernames);
//...
}

Is it possible to retrieve the element "usersSuppr []" without having to use a ? Because I already use 2 in my twig file for other features and I can not add this feature with a because it would be a problem, it would mix with others