Invalid variable $release used in @initrd macro for FreeBSD
The @initrd macro defined for FreeBSD here) uses the variable '$release', which only exists for Debian and Solaris systems, according to the documentation. For me, this results in the following path: boot/FreeBSD-x86_64--mfs.img
This should probably be boot/FreeBSD-x86_64-12.0-mfs.img
I suppose the fix should be as simple as substituting the $release variable for the $version variable.