rev-parse --show-cdup in .git

I'm sure this was discussed somewhere, but I can't find it:

When called from within .git, git rev-parse --show-cdup returns nothing rather than "..", not even an error code. Is this intended?

This is all the more disturbing since the cwd of hooks seems to be GIT_DIR. Is that something one can rely upon? In that case one can simply use ".." for cdup.

Michael

P.S.: The use case is a simple post-receive-hook that fast forwards a checked out branch on receiving refs in refs/remotes/incoming/, but needs to check the worktree against the index etc. 1.7.0 may be an opportunity to encourage usage of this rather than restoring the old behavior through options.