accumulateEvent is passed the event from the piluep file.  I don't think ```edm::Refs``` are functional from the pileup files. Therefore @giamman when you loop over the Tracks, you can not call any method which would dereference the ```RefToBase<TrackExtra>```. Instead, you must get the ```TrackExtra``` from the ```TrackExtra``` collection at the same index as the ```Track```. You will then be able to get information from that directly.