Hi,
I think I've found a syntax error while watching the code to understand how it works. The line is:
GRUB_DISABLE_LINUX_PARTUUID=${GRUB_DISABLE_LINUX_PARTUUID-true}
and I guess it should be:
GRUB_DISABLE_LINUX_PARTUUID=${GRUB_DISABLE_LINUX_PARTUUID:-true}
It can be found in 10_linux:48 and 20_linux_xen:48.
Hope this helps and thanks for your hard work,
Alejandro Lopez