MariaDB Rejects NULL Literal as Default Argument in LAG Window Function

CREATE DATABASE lagtest; USE lagtest;

CREATE TABLE llt (id INT PRIMARY KEY, p INT, o INT, v INT);

INSERT INTO llt VALUES (1,1,10,5),(2,1,20,7),(3,1,30,9);

-- OK: 2-argument form (implicit NULL)

SELECT LAG(v, 1) OVER (PARTITION BY p ORDER BY o) FROM llt;

-- OK: 3-argument form with integer default

SELECT LAG(v, 1, 0) OVER (PARTITION BY p ORDER BY o) FROM llt;

-- FAIL: 3-argument form with NULL literal

SELECT LAG(v, 1, NULL) OVER (PARTITION BY p ORDER BY o) FROM llt;

-- ERROR 1064 (42000): syntax error near ' NULL) OVER (...)'