DecayTreeFitterAlg requires LHCb::RecVertex
See mattermost starting from https://mattermost.web.cern.ch/lhcb/pl/hiim6cn4bpnyubjbnm4g33piyh by @yamhis
The workaround is
conf = PersistRecoConf.PersistRecoPacking(stream='/Event/' + stream_pvs, data_type=data_type)
pvs_v1 = conf.unpackers_by_key()["PVs"]
by @sstahl .
It is decided not to fix for the time being because DecayTreeFit::Fitter needs LHCb::VertexBase which v2::RecVertex does not implement. It will be fixed once the event model is stable.