Patrick Steinhardt [off-list ref] writes:

+	if (repo_get_oid_with_flags(repo, argv[1], &newoid, GET_OID_SKIP_AMBIGUITY_CHECK))
+		die(_("invalid object ID: '%s'"), argv[1]);
+	if (is_null_oid(&newoid))
+		die(_("cannot create reference with null old object ID"));

An apparent typo here, "with null old" -> "with null new object
name".

Other than that, I think this one is good.