diff -b / -w and empty diffs

Hello!

If the difference between two files is only whitespace, "git diff -b"
leads to diffs just consisting of the "diff" and "index" lines. I would
like an option to suppress those files in the diff output because it
breaks "git diff -b > patch; git apply patch" workflows (and often I'm
just interested in "real" changes).

Is there any reason why such behaviour is not implemented yet (besides
the fact that nobody cared to do it)?