Make spotless pre-commit script work? Possibly? Can't verify until di…

…ffplug/spotless#2365 is fixed.

spotless/pre-commit

@@ -1,13 +1,25 @@
+#!/bin/sh
+
 # Runs spotlessApply on staged changes. This script is intended to be used as a pre-commit hook.
 # To use it, copy this script to .git/hooks/pre-commit and make it executable.
 # For more samples / inspiration check:
 # https://github.com/diffplug/spotless/issues/178
 # https://github.com/diffplug/spotless/issues/623
+#
+# Can't reliably verify if it works until
+# https://github.com/diffplug/spotless/issues/2365
+# Is fixed
 
-#!/usr/bin/env bash
 set -euo pipefail
 
-RATCHET_REF="${HEAD^}"
+if git rev-parse --verify HEAD >/dev/null 2>&1
+then
+	RATCHET_REF=HEAD
+else
+	# Initial commit: diff against an empty tree object
+	RATCHET_REF=$(git hash-object -t tree /dev/null)
+fi
+
 echo "Running spotlessApply on files changed since ${RATCHET_REF}"
 
 ./gradlew --no-daemon --console=plain :spotlessApply -PratchetFrom="${RATCHET_REF}"