manager: Use STR_IS_NULL_OR_EMPTY macro

src/calls-manager.c

@@ -1072,7 +1072,7 @@ calls_manager_get_origin_by_id (CallsManager *self,
   g_return_val_if_fail (CALLS_IS_MANAGER (self), NULL);
 
   /* TODO Turn this into a critical once https://gitlab.gnome.org/GNOME/calls/-/merge_requests/505 is in */
-  if (origin_id && *origin_id)
+  if (STR_IS_NULL_OR_EMPTY (origin_id))
     return NULL;
 
   n_origins = g_list_model_get_n_items (G_LIST_MODEL (self->origins));