The tag is present in Lintian version 2.104.234. That is the most recent version we know about.
Homepage field in this package's
control file refers to Rubygems, and not to the true upstream.
Debian packages should point at the upstream's homepage, but
Rubygems is just another packaging system. You may be able to
find the correct information in the
of the corresponding Rubygems package.
Refer to Bug#981935 for details.