Hi,
Thanks for the feedback.
Change that line from:
$l = str_replace('{'.strtoupper($k).'}', $v, $l);
to:
$l = str_replace('{'.strtoupper($k).'}', (string)$v, $l);
and it will remove the message. We'll addd the change on our end for the next version of HikaShop which is to be released soon.