With commit 4e5fe9ad19, range partition missing handling for the NULL partition key

Consider the below test:

CREATE TABLE range_tab(a int, b int) PARTITION BY RANGE(a);
CREATE TABLE range_tab_p1 PARTITION OF range_tab FOR VALUES FROM (minvalue)
TO (10);
CREATE TABLE range_tab_p2 PARTITION OF range_tab FOR VALUES FROM (10) TO
(20);
CREATE TABLE range_tab_p3 PARTITION OF range_tab FOR VALUES FROM (20) TO
(maxvalue);

INSERT INTO range_tab VALUES(NULL, 10);

Above insert should fail with an error "no partition of relation found for
row".

Looking further I found that, this behaviour is changed after below commit:

commit 4e5fe9ad19e14af360de7970caa8b150436c9dec
Author: Robert Haas <rhaas(at)postgresql(dot)org>
Date: Wed Nov 15 10:23:28 2017 -0500

Centralize executor-related partitioning code.

Some code is moved from partition.c, which has grown very quickly
lately;
splitting the executor parts out might help to keep it from getting
totally out of control. Other code is moved from execMain.c. All is
moved to a new file execPartition.c. get_partition_for_tuple now has
a new interface that more clearly separates executor concerns from
generic concerns.

Amit Langote. A slight comment tweak by me.

Before above commit insert with NULL partition key in the range partition
was throwing a proper error.

postgres(at)112171=#INSERT INTO range_tab VALUES(NULL, 10);
ERROR: no partition of relation "range_tab" found for row
DETAIL: Partition key of the failing row contains (a) = (null).

Looking at the code partition_bound_cmp(), before 4e5fe9ad19 commit there
was a condition for the null values:

/*
* No range includes NULL, so this will be accepted by
the
* default partition if there is one, and otherwise
* rejected.
*/
for (i = 0; i < key->partnatts; i++)
{
if (isnull[i] &&

partition_bound_has_default(partdesc->boundinfo))
{
range_partkey_has_null = true;
break;
}

* else if (isnull[i]) {
*failed_at = parent;
*failed_slot = slot; result = -1;
goto error_exit; }* }

But after commit, condition for isnull is missing. It doesn't look
intentional,
is it?

Attaching patch to fix as well as regression test.

Thanks,
Rushabh Lathia
www.EnterpriseDB.com