Merge pull request #612 from diffplug/feat/ratchet-fix

Fix GitRatchet for the case where a non-existent reference is specified.

Author: nedtwigg

plugin-gradle/CHANGES.md

@@ -10,6 +10,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
   * Bumped default versions, prettier `1.16.4` -> `2.0.5`, tslint `5.12.1` -> `6.1.2`
 ### Fixed
 * Using `ratchetFrom 'origin/main'` on a bare checkout generated a cryptic error, now generates a clear error. ([#608](https://github.com/diffplug/spotless/issues/608))
+* Using `ratchetFrom 'nonexistent-reference` generated a cryptic error, now generates a clear error. ([#612](https://github.com/diffplug/spotless/issues/612))
 
 ## [4.3.0] - 2020-06-05
 ### Deprecated

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/GitRatchet.java

@@ -186,6 +186,9 @@ public synchronized ObjectId rootTreeShaOf(Project project, String reference) {
 			ObjectId treeSha = rootTreeShaCache.get(repo, reference);
 			if (treeSha == null) {
 				ObjectId commitSha = repo.resolve(reference);
+				if (commitSha == null) {
+					throw new IllegalArgumentException("No such reference '" + reference + "'");
+				}
 				try (RevWalk revWalk = new RevWalk(repo)) {
 					RevCommit revCommit = revWalk.parseCommit(commitSha);
 					treeSha = revCommit.getTree();