All reports of license-problem-gfdl-invariants-empty for the archive. The extended description of this tag is:
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. .
Refer to https://wiki.debian.org/qa.debian.org/gfdlinvariant and https://www.debian.org/vote/2006/vote_001 for details.
This tag has not been emitted in any package tested by Lintian.