UNWIND $keys AS key
OPTIONAL MATCH (nrsr:NrSoundRecording:NrPerformance { id: key.id })
OPTIONAL MATCH (nrsr)<-[:CONTRIBUTED_TO]-(nrc:NrContribution:NrPerformance)
WHERE (key.valid IS null OR nrc.valid = key.valid)
RETURN key, collect(nrc{ .id }) AS contributions;