The given source file is licensed under GFDL, but without any precision about the presence of invariant sections, front-cover or back-cover text.
GFDL license explicitly requests you to document this non-presence.
For more information please consult:
The tag is present in Lintian version
That is the most recent version we know about.
We use semantic versions.
The patch number is a commit step indicator relative to the
release tag in our Git
You can find the detection logic for this version at commit 43a81d7. For merge requests, please use the latest version in the Lintian check cruft.