Reduced from sqlsmith, this query fails under debug_parallel_query=1. The elog was added at: 55416b26a98fcf354af88cdd27fc2e045453b68a But (I'm not sure) the faulty commit may be 8edd0e7946 (Suppress Append and MergeAppend plan nodes that have a single child).
postgres=# SET force_parallel_mode =1; CREATE TABLE x (i int) PARTITION BY RANGE (i); CREATE TABLE x1 PARTITION OF x DEFAULT ; select * from pg_class, lateral (select pg_catalog.bit_and(1) from pg_class as sample_1 where case when EXISTS ( select 1 from x where EXISTS ( select 1 from pg_catalog.pg_depend where (sample_1.reltuples is NULL) )) then 1 end is NULL)x where false; -- Justin