negative bitmapset member not allowed Error with partition pruning

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postgres=# SET enable_partition_pruning TO on;
SET
postgres=# CREATE TABLE part (a INT, b INT) PARTITION BY LIST(a);
CREATE TABLE
postgres=# CREATE TABLE part_p1 PARTITION OF part FOR VALUES IN (-2,-1,0,1,2);
CREATE TABLE
postgres=# CREATE TABLE part_p2 PARTITION OF part DEFAULT PARTITION BY RANGE(a);
CREATE TABLE
postgres=# CREATE TABLE part_p2_p1 PARTITION OF part_p2 DEFAULT;
CREATE TABLE
postgres=# INSERT INTO part VALUES (-1,-1),(1,1),(2,NULL),(NULL,-2),(NULL,NULL);
INSERT 0 5
postgres=# EXPLAIN (COSTS OFF)
postgres-# SELECT tableoid::regclass as part, a, b FROM part WHERE a IS NULL ORDER BY 1, 2, 3;
ERROR:  negative bitmapset member not allowed
postgres=# SET enable_partition_pruning TO off;
SET
postgres=# EXPLAIN (COSTS OFF)
SELECT tableoid::regclass as part, a, b FROM part WHERE a IS NULL ORDER BY 1, 2, 3;
                               QUERY PLAN                              
------------------------------------------------------------------------
 Sort
   Sort Key: ((part_p1.tableoid)::regclass), part_p1.a, part_p1.b
   ->  Append
         ->  Seq Scan on part_p1
               Filter: (a IS NULL)
         ->  Seq Scan on part_p2_p1
               Filter: (a IS NULL)
(7 rows)

postgres=#