The tag is present in Lintian version 2.104.264. That is the most recent version we know about.
The package appears to be licensed under the Apache 2.0 license and
NOTICE file (or similar) exists in the source tree. However, no
NOTICE.txt are installed in any
of the binary packages.
The Apache 2.0 license requires distributing of such files:
(d) If the Work includes a "NOTICE" text file as part of its distribution, then any Derivative Works that You distribute must include a readable copy of the attribution notices contained within such NOTICE file [..]
Please include the file in your package, for example by adding
path/to/NOTICE to a
Refer to /usr/share/common-licenses/Apache-2.0 for details.