Dear Maintainer,
in /usr/lib/apt/apt.systemd.daily all vars defined by eval + apt-config
shell are pre-initialized, except the one used for daily_lock file.
Cache="/var/cache/apt/archives/"
eval $(apt-config shell Cache Dir::Cache::archives/d)
versus
eval $(apt-config shell StateDir Dir::State/d)
exec 3>${StateDir}/daily_lock
So if apt-config shell fails, $StateDir is undefined, daily_lock is
created in / instead of /var/lib/apt/
so you can have something like that: