Since it's serialized as `to_json`, see https://github.com/psu-stewardship/active_fedora_relsint/blob/1ef27a9c0531e3d59854814a886ef1de467b038c/lib/active_fedora_relsint/datastream.rb#L139, we probably need to deserialize it from json.  Maybe a round-trip serizlize then deserialize test is in order.