avoid ''NoneType' object has no attribute 'exists'' error when purging models

database_cleanup/model/purge_models.py

@@ -65,8 +65,10 @@ class CleanupPurgeLineModel(orm.TransientModel):
             row = cr.fetchone()
             if row:
                 self.logger.info('Purging model %s', row[1])
-                attachment_ids = attachment_pool.search(
-                    cr, uid, [('res_model', '=', line.name)], context=context)
+                cr.execute(
+                    "UPDATE ir_attachment SET res_model = FALSE "
+                    "WHERE id in %s",
+                    (tuple(attachment_ids), ))
                 if attachment_ids:
                     attachment_pool.write(
                         cr, uid, attachment_ids, {'res_model': False},