Hi,
The line 63 is
foreach($formData['serial'] as $col => $val) {
If you do not have the index "serial" in the variable "formData" it means that the form is not submitted correctly.
So you're not saving anything in the serial.
I'm afraid that you have another kind of problem which is breaking the serial edition form in your backend.
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.