cartads: don't crash on dossier types without any subjects (#33506)

passerelle/apps/cartads_cs/models.py

@@ -158,7 +158,7 @@ class AbstractCartaDSCS(BaseResource):
     def objets_demande(self, request, type_dossier_id):
         client = self.soap_client()
         resp = client.service.GetObjetsDemande(self.get_token(), type_dossier_id)
-        return {'data': [{'id': str(x['Key']), 'text': x['Value']} for x in resp]}
+        return {'data': [{'id': str(x['Key']), 'text': x['Value']} for x in resp or []]}
 
     @endpoint(description=_('Get list of CERFA documents'),
               parameters={