BUG #17298: Error in func pg_get_serial_sequence()

The following bug has been logged on the website:

Bug reference: 17298
Logged by: Serge Salamatin
Email address: salamsp(at)gmail(dot)com
PostgreSQL version: 13.5
Operating system: Ubuntu 13.5-2.pgdg20.04+1
Description:

CREATE SEQUENCE IF NOT EXISTS tnd.ui_seq
INCREMENT 1
START 1
MINVALUE 1
MAXVALUE 9223372036854775807
CACHE 1;

CREATE TABLE IF NOT EXISTS tnd.xdwdef
(
defnm citext COLLATE pg_catalog."default" NOT NULL,
ui_id bigint NOT NULL DEFAULT nextval('tnd.ui_seq'::regclass),
def citext COLLATE pg_catalog."default",
CONSTRAINT defnm_pk PRIMARY KEY (defnm)
)

;
select pg_get_serial_sequence('tnd.xdwdef','ui_id');

returns null