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@gmail.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