On writing builtin-reset.c, a question about git-reset.sh

Hi, I'm writing builtin-reset.c and I'm really stuck with a little code in git-reset.sh:

if orig=$(git rev-parse --verify HEAD 2>/dev/null)
then
	echo "$orig" >"$GIT_DIR/ORIG_HEAD"
else
	rm -f "$GIT_DIR/ORIG_HEAD"
fi

My question is about when this condition could fail (and then the rm executed), and if you would be able to reproduce it in tests. I couldn't, and asking for this in the IRC didn't help me at all.

This code was introduced in 45d197, when different reset types were introduced, and it seems that there was a reason for doing it that way, looking at the change.

Thanks in advance for your support.

-- Carlos