function upsert inserting null values - database

Question

I created the following function upsert(insert or edit if it's already exist) in postgresql using pgadmin 4.
CREATE OR REPLACE FUNCTION upsert(
uname character varying(55),
fname character varying(55),
eml character varying(255),
psw character varying(265),
phonenbr character varying(55),
adrs character varying(300)
)
RETURNS table (j json) AS
$$
BEGIN
INSERT INTO users
VALUES (DEFAULT,uname, fname, eml, psw, phonenbr, adrs)
ON CONFLICT (username, firstname)
DO
UPDATE SET username = EXCLUDED.username, firstname = EXCLUDED.firstname,
email = EXCLUDED.email, password = EXCLUDED.password, phonenumber = EXCLUDED.phonenumber,
address = EXCLUDED.address, registrationdate=current_timestamp, subscriptionend =current_timestamp+ INTERVAL '1 month',stat='active';
END
$$
LANGUAGE 'plpgsql';
The issue is than when it's doing an insert, for 3 column the values are null but everything it's fine when it's doing an update.
He there a way to solved this issue without adding 3 more parameters to the function ?
the scrip for create the table:
CREATE TABLE users
(
id_user integer Generated Always as Identity,
username character varying(55) NOT NULL,
firstname character varying(55) NOT NULL,
email character varying(255) NOT NULL,
password character varying(255)NOT NULL,
phonenumber character varying(55)NOT NULL,
address character varying(300) NOT NULL,
subscriptionend timestamp without time zone ,
registrationdate timestamp without time zone,
stat status,
CONSTRAINT users_pkey PRIMARY KEY (username,firstname)
)

Answer 1

I find a solution by declaring and using variables inside the function:
CREATE OR REPLACE FUNCTION upsert(
uname character varying(55),
fname character varying(55),
eml character varying(255),
psw character varying(265),
phonenbr character varying(55),
adrs character varying(300)
)
RETURNS table (j json) AS
$$
DECLARE
regisdate timestamp without time zone;
subsend timestamp without time zone;
statu status;
BEGIN
regisdate:=current_timestamp;
subsend:=current_timestamp+ INTERVAL '1 month';
statu='active';
INSERT INTO users
VALUES (DEFAULT,uname, fname, eml, psw, phonenbr, adrs,regisdate,subsend,statu)
ON CONFLICT (username, firstname)
DO
UPDATE SET username = EXCLUDED.username, firstname = EXCLUDED.firstname,
email = EXCLUDED.email, password = EXCLUDED.password, phonenumber = EXCLUDED.phonenumber,
address = EXCLUDED.address, registrationdate = EXCLUDED.registrationdate, subscriptionend=EXCLUDED.subscriptionend,stat = EXCLUDED.stat;
END
$$
LANGUAGE 'plpgsql';