Hello Neels,
i have checked back with pau. A codec list with 0 elekents is indeed permitted. So I will now change this. In osmo-bsc I will then remove the check, so if the config does not permit any codecs the codec list will have 0 elements.
However, we could also just interpret the spec differently. If we support 0 codecs the network wouln't be able to support an IP based user plane interface and therefore the codec list does not have to be included.
So in fact we found a solution now. I will keep you posted on this.
best regards, Philipp