Notice: Undefined property:

-- HikaShop version -- : latest
-- Joomla version -- : 3.4
-- PHP version -- : 5.6.14-1+deb.sury.org~trusty+1
-- Browser(s) name and version -- : firewfox
-- Error-message(debug-mod must be tuned on) -- : Notice: Undefined property: stdClass::$user_email in /www/media/com_hikashop/mail/waitlist_admin_notification.preload.php on line
35

Hallo.

I get this error messages in the email notification for the productwaitlist. What does this mean?

thanks for reply