Wrong results from Parallel Hash Full Join

[Richard Guo]

I came across $subject and reduced the repro query as below.

create table a (i int);
create table b (i int);
insert into a values (1);
insert into b values (2);
update b set i = 2;

set min_parallel_table_scan_size to 0;
set parallel_tuple_cost to 0;
set parallel_setup_cost to 0;

# explain (costs off) select * from a full join b on a.i = b.i;
                QUERY PLAN
------------------------------------------
 Gather
   Workers Planned: 2
   ->  Parallel Hash Full Join
         Hash Cond: (a.i = b.i)
         ->  Parallel Seq Scan on a
         ->  Parallel Hash
               ->  Parallel Seq Scan on b
(7 rows)

# select * from a full join b on a.i = b.i;
 i | i
---+---
 1 |
(1 row)

Tuple (NULL, 2) is missing from the results.

Thanks
Richard