BUG #18139: Causing FATAL error on database using function last() or first()

The following bug has been logged on the website:

Bug reference: 18139
Logged by: Paul Gazagne
Email address: pyrotarlu74(at)gmail(dot)com
PostgreSQL version: 14.9
Operating system: (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, 64-bit
Description:

How to reproduce the error :

Setup table and dataset :
CREATE TABLE test (
id int4 not null,
value numeric(20, 6) NULL,
value_t text NULL
);

INSERT INTO test (id)
VALUES (1);
INSERT INTO test (id,value,value_t)
VALUES (2,2,'it is 2');
INSERT INTO test (id)
VALUES (3);
INSERT INTO test (id,value,value_t)
VALUES (4,4,'it is 4');
INSERT INTO test (id)
VALUES (5);

If I use the function last/first on this dataset, if the first rows parsed
by the function contain null values, it cause FATAL error on database.

Examples :
These queries work fine :

select
last(value_t,value) as thatsok
from test t
where id between 2 and 4;

select
last(value_t,value) as thatsok
from test t
where id between 2 and 5;

select
first(value_t,value) as thatsok
from test t
where id between 2 and 4;

select
first(value_t,value) as thatsok
from test t
where id between 2 and 5;

These ones cause FATAL error :

select
last(value_t,value) as fatal_error
from test t
where id between 1 and 5;

select
first(value_t,value) as fatal_error
from test t
where id between 1 and 5;