The tag is present in Lintian version 2.104.318. That is the most recent version we know about.
The paragraph has a "License" and a "Copyright" field, but no "Files" field. Technically, this is a valid paragraph per the DEP 5 specification. However, it is mostly likely a mistake.
If it is a
stand-alone license paragraph, the "Copyright"
field is not needed and should be removed. On the other hand, if it
files paragraph, it is missing the "Files" field.
Please note that while the "Files" field was optional in some cases
in some of the earlier draft versions, it is mandatory in all
files paragraphs in the current specification.
Lintian will attempt to guess what you intended and continue based on its guess. If the guess is wrong, you may see spurious tags related to this paragraph.
Please refer to Bug#652380 and https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/ for details.