SQL Custom Function is not returning data as expected by matching to my conditions

I am trying to create this function but null values fail

CREATE OR REPLACE function func(inspection_date date, strike_time date, taskaction_display varchar, last_known_status varchar, severity int)
RETURNS TABLE(last_known_task_status varchar, taskaction int) AS $$
    SELECT CASE
        WHEN inspection_date IS null THEN (taskaction_display, severity)
        WHEN strike_time >= inspection_date THEN (taskaction_display, severity)
        WHEN ((strike_time BETWEEN inspection_date - INTERVAL '6' MONTH AND inspection_date) AND last_known_status IS NOT null) THEN (last_known_status, 
             CASE
                WHEN last_known_status = 'IN_PROGRESS' THEN 11
                WHEN last_known_status = 'PENDING' THEN 12
                WHEN last_known_status = 'COMPLETE' THEN 13
                WHEN last_known_status = '' THEN -1
                ELSE -2
             END)
        WHEN ((strike_time BETWEEN inspection_date::date - INTERVAL '6' MONTH AND inspection_date) AND last_known_status IS null) THEN ('REVIEWED'::text, -3)
        WHEN (strike_time < inspection_date - INTERVAL '6' MONTH) THEN ('REVIEWED'::text, -2)
        ELSE ('NO MATCH'::text, -4)
    END
$$
language sql stable;

But some of the conditions are not working, specially when I am passing null calls that are not giving expected results are:

SELECT * FROM func('2022-03-22', '2022-01-22',
'strike in six months before inspection + last_known_status = null',
null, 20)

Expecting above to return (‘REVIEWED’, -2) while I am getting nothing

SELECT * FROM func(null, '2021-01-22',
'strike time older than inspection date by more than 6 months but inspection_date is null',
'IS_NULL', 11)

Expecting above to return ( , -2) while I am getting nothing

SELECT * FROM func('2022-03-22', '2021-01-22',
'strike in six months before inspection + last_known_status = IN_PROGRESS',
'IN_PROGRESS', 20)

Expecting above to return (‘IN_PROGRESS’, 11) while I am getting (“NO MATCH”, -4)

In simple words the following is what I am trying to achieve A SQL function that takes in

func(inspection date, strike date, action varchar, status varchar, severity int)

And returns the following based on conditions

if(inspection == null) return (action, severity)
else if(strike >= inspection) return (action, severity)
else if(strike >= inspection-6 months) {
    if(status == null) return ('REVIEWED', -1)
    else if(status == 'IN_PROGRESS') return (status, 11)
    else if(status == 'PENDING') return (status, 12)
    else if(status == 'COMPLETE') return (status, 13)
    else ('NO STATUS MATCH', -2)
}
else if(strike < inspection-6 months) return ('REVIEWED', -3)
else return ('NO MATCH', -4)

Answer

I explain null case only. Your code working as intended. If you not sure. just copy paste all the work in sql fiddle.
demo

SELECT * FROM func(null, '2021-01-22',
'strike time older than inspection date by more than 6 months but inspection_date is null',
'IS_NULL', 11)

will return

                               last_known_task_status                                  | taskaction
------------------------------------------------------------------------------------------+------------
 strike time older than inspection date by more than 6 months but inspection_date is null |         11

BECAUSE: This execution meet predicate:

WHEN inspection_date IS null THEN (taskaction_display, severity)

---

SELECT * FROM func('2022-03-22', '2022-01-22',
'strike in six months before inspection + last_known_status = null',
null, 20);

will get

 last_known_task_status | taskaction
------------------------+------------
 REVIEWED               |         -2

BECAUSE It meet predicate

WHEN ((strike_time BETWEEN inspection_date::date - INTERVAL '6' MONTH AND inspection_date)
                  AND last_known_status IS null) THEN ('REVIEWED'::text, -2)