There _is_ no source file to claim copyright on in this case
Sorry, but that's just not true. SCOTUS has already upheld the copyright protection on the 11,500 lines of source code. It's not from thin air. It was authored by Sun and copied/distributed by Google, despite the "DO NOT DISTRIBUTE!" copyright license file direction.
This 'generated' code issue is a red-herring; it's not part of Google's fair-use argument. Javadoc is generated from the code, not the other way around. Google copied the copyrighted source code.