NPE in queries with a project on a subquery with Union all

The following query (data file attached) causes a NPE:

select trans_id from
(
select trans_id, trans_id as ti from dfs.`mobile-small-copy.json.gz` where trans_id = 19999
union all
select trans_id, trans_id as ti from dfs.`mobile-small-copy.json.gz` where trans_id = 19998
)