[PrestaShop] Fatal error in module includes: Undefined index: HTTP_HTTPS

[Bocko]

I moved from a Litespeed to an Apache server today. And it works very well so far, it made it possible for me to lower load time with like 70% all-in-all.

 

However, I THINK this error occured after the move. At least I haven't nocticed it before. At the bottom of list of modules it says:

 

[PrestaShop] Fatal error in module includes:

Undefined index: HTTP_HTTPS

 

What does this mean? I've uninstalled/deleted some modules I'll never use. Might that be it, or is it something about the switch from Litespeed to Apache? Some settings? Some php.ini or .htaccess thing?