Set variable if variable didn't initialized

I'm creating alternate of uuid_short() function named custom_uuid_short.

DELIMITER $$
CREATE DEFINER=`root`@`localhost` FUNCTION `custom_short_uuid`() RETURNS bigint(20) unsigned
BEGIN
    declare shorty bigint(20) unsigned;
    set shorty = 100;

    SET @incremented_variable:=@incremented_variable+1;

    SELECT (((525190530 & 255) << 56) + (Uptime << 24) + @incremented_variable) into shorty
    FROM     
        (SELECT variable_value Uptime 
            FROM information_schema.global_status
            WHERE variable_name = 'Uptime_since_flush_status') up;

    RETURN @incremented_variable;
END

The problem is @incemented_variable will be null when i create this function on new database.

Is there any way to do initialize the variable if not initialized in the funtion itself?