Making custom git-remove-tree command

I'm doing a script named git-remove-tree which removes the working tree known to Git. It doesn't touch untracked files; it only deletes directories if they are empty. The script seems to work, but because I'm not very good at Git plumbing and there can be some corner cases which I don't know about, I'd appreciate if more experienced users would have a look. Is the following script safe?

#!/bin/sh # git-remove-tree

is_wt=$(git rev-parse --is-inside-work-tree)
if [ "$is_wt" = false ]; then
	echo "You must run this inside a working tree."
	exit 1
elif [ -z "$is_wt" ]; then
	exit 1
fi

top=$(git rev-parse --show-toplevel)
cd "$top" || {
	echo "Can't go to top-level directory $top"
	exit 1
}

git ls-tree --name-only -r -z HEAD | xargs -0r -- sh -c '
for f in "$@"; do
	rm -f -- "$f"
	d=$(dirname -- "$f")
	[ "$d" = . ] || rmdir -p -- "$d" 2>/dev/null
done' dollar0_argument

echo 'Use "git reset --hard HEAD" to populate the working tree again.'