The bug is not really in gcj, it's in a script in gcc-defaults, which ends up in the binary named gcj-jdk for some bizarre reason.
However, I've just been looking further, and it looks like the script is literally only used by jaminid, and that jaminid looks pretty abandoned upstream, and has no deps or rdeps, and the maintainer is idle. So maybe both can be removed, and the archive can be a better place. https://codesearch.debian.net/search?q=dh_javadoc+path%3Adebian%2Frules
