BUG #15311: Incorrect comparison of the empty array with the value of the custom type from the table field

The following bug has been logged on the website:

Bug reference: 15311
Logged by: Виктор Васильев
Email address: vvvasilev93(at)gmail(dot)com
PostgreSQL version: 10.4
Operating system: Ubuntu 16.04 LTS
Description:

test_db=> select version()
PostgreSQL 10.4 (Ubuntu 10.4-2.pgdg16.04+1) on i686-pc-linux-gnu, compiled
by gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609, 32-bit

test_db=> create type type_mnemonic as enum ('ex', 'in');
CREATE TYPE

test_db=> create table tbl_for_tst(id integer, type type_mnemonic[]);
CREATE TABLE

test_db=> insert into tbl_for_tst(id, type) values (1, '{ex}'), (2, '{in}'),
(3, '{ex}'), (4, '{in}');
INSERT 0 4

test_db=> select * from tbl_for_tst;
id | type
----+------
1 | {ex}
2 | {in}
3 | {ex}
4 | {in}
(4 строки)

test_db=> do $$
declare
r tbl_for_tst;
vtbl_for_tst jsonb;
adata jsonb := '{"type":[]}';
begin
select to_jsonb(e)
into vtbl_for_tst
from tbl_for_tst e
where e.id = 1;

r := jsonb_populate_record(r, vtbl_for_tst || adata);

update tbl_for_tst e
set type = r.type
where e.id = 1;
end;
$$;
DO

test_db=> select id, type, type = '{}' as res from tbl_for_tst;
id | type | res
----+------+----------
2 | {in} | f
3 | {ex} | f
4 | {in} | f
1 | {} | f
(4 строки)

test_db=> update tbl_for_tst set type = '{}' where id = 4;
UPDATE 1

test_db=> select id, type, type = '{}' as res from tbl_for_tst;
id | type | res
----+------+----------
2 | {in} | f
3 | {ex} | f
1 | {} | f
4 | {} | t
(4 строки)