Aggregate stored function return always NULL in case of empty input set

DELIMITER //

-- Function created as per documentation:

-- https://mariadb.com/kb/en/stored-aggregate-functions/#examples

CREATE AGGREGATE FUNCTION aggregate_count(x INT) RETURNS INT

BEGIN

	DECLARE count_students INT DEFAULT 0;

	DECLARE CONTINUE HANDLER FOR NOT FOUND RETURN count_students;

 	LOOP

		FETCH GROUP NEXT ROW;

		IF x  THEN

			SET count_students = count_students+1;

		END IF;

	END LOOP;

END //

-- Nominal case (no where clause)

WITH q(v) AS (

	VALUES

	(0),

	(1),

	(2)

)

SELECT COUNT(NULLIF(v, 1)), aggregate_count(v)

FROM q

//

-- Error case: no value are available in input

WITH q(v) AS (

	VALUES

	(0),

	(1),

	(2)

)

SELECT COUNT(NULLIF(v, 1)), aggregate_count(v)

FROM q

WHERE FALSE 

//

DROP FUNCTION aggregate_count //

DELIMITER ;