CASE with identical COUNT(*) branches makes a nested empty-input aggregate predicate return NULL instead of TRUE

While testing MariaDB 11.8.9, I came across an interesting result discrepancy involving a user variable (@v) in a nested COUNT(*) query. Two equivalent forms return different results: one returns a row, while the other returns an empty set. The reduced test case is shown below.

CREATE TABLE t (a INT) ENGINE=InnoDB;

SET @v = '';

SELECT 1 AS result

WHERE (

SELECT COUNT() = (

(SELECT COUNT() FROM (SELECT 1) d) - 1

)

FROM t

);

SELECT 1 AS result

WHERE (

SELECT COUNT() = (

(

SELECT CASE

WHEN (SELECT COUNT() FROM (SELECT @v AS a) s)

THEN COUNT()

ELSE COUNT()

END

FROM (SELECT 1) d

) - 1

)

FROM t

);

Actual result on 11.8.9-MariaDB:

The first query returns:

result

1

The second query returns:

Empty set

Expected result:

Both queries should return one row:

result

1