JOSM throws error on hgv turn restriction

I have added a relation in JOSM with the following properties:

type=restriction
restriction:hgv=only_left_turn

The members are the junction node as “via”, and a “from” and “to” way.

When I try to upload the data to the server, JOSM throws an error (not a warning) saying “Unbekannte Abbiegebeschränkung” (german fpr “unknown turn relation”.

If I remove the “:hgv”, there is no error.

But the restriction applies only to HGVs, and according to the OSM Wiki, I am doing everything right (at least I cannot see anything wrong).

Is this an error in JOSM, or am I doing it wrong?

It seems to be that JOSM validator does not support it.
You can report here

As a side note, isn’t it better to map this as hgv=no on all the other roads at that junction? Routers are more likely to support the access restriction than a conditional turn restriction. Or are HGVs allowed to turn into those roads from other directions?