Hi,
It means that something (HikaShop, a plugin, or else) is trying to send an email but no destination email has been provided.
Please check that your HikaShop configuration is right full configured for the email part (where you can specify the email which will receive email notification for example).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.