The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
The classpath listed in the jar file refers to a potential missing jar file. This could be the remnants of a build-time classpath that are not relevant for a JAR bundled in a Debian package.
Alternatively, the classpath may be correct, but the package is lacking a jar file or a symlink to it.
Note, Lintian assumes that all (relative) classpaths pointing to /usr/share/java/ (but not subdirs thereof) are satisfied by dependencies as long as there is at least one strong libX-java dependency.