Is "show-ref -h" a good test for an empty repository?

Hi,

I'm trying to test to see if "git diff --cached" will fail because there are no existing commits. I've come up with running "git show-ref -h -q" and testing its return value. My hypothesis is: If and only if git-show-ref succeeds then git-diff will succeed.

Are my logic and assumptions sound? I'm a bit out of my git comfort zone here, so I'd like to get some validation from some people who know better.

Thanks in advance for the help!

Cheers,