A quick bit of Cypher demonstrating how you can change the default null-ordering in ORDER BY. Note that the trick is in the null predicate and STR cast.

gistfile1.txt

START n=node({startId})
MATCH (n)-[?:DID]->(thing)
WITH thing, (thing.year? = null) AS year_is_null
WITH thing, STR(year_is_null) as null_year
ORDER BY null_year, thing.year? DESC
RETURN thing, thing.year? as year