Por que recebo Nulo deste procedimento armazenado?

DELIMITER $$
CREATE PROCEDURE GetName(IN kartennummer CHAR(16), OUT name VARCHAR(91))
BEGIN
    SELECT 
        CONCAT_WS(' ', Vorname, Nachname)
        INTO 
        name
    FROM
        Kunden kund
            JOIN
        Konten kont
    WHERE
        kund.KundenID = kont.KundenID
            AND kont.Kartennummer = kartennummer;
END;
DELIMITER ;