The version file no longer exist in the named kernel folder.
Unless it is decided to include kernel-headers in Packages-Root the local _kernver variable must be read from elsewhere
issue #343 (closed) suggest reading /boot/*kver
The MR suggests reading the kernelbase file in the named kernel folder and parse the version using awk
local _kernver=$(cat $1/usr/lib/modules/*/kernelbase | awk -F'-' '{print $1}')