untracked-cache: be defensive about missing NULs in index

diff --git a/t/t4027-diff-submodule.sh b/t/t4027-diff-submodule.sh
index e5f9eb7a11f0e5bba35b024bfffc4f175e889433..9aa8e2b39b45a6c2b5ec48a9d98b94831edb2caa 100755 (executable)
--- a/t/t4027-diff-submodule.sh
+++ b/t/t4027-diff-submodule.sh
@@ -239,10 +239,9 @@ test_expect_success 'git diff between submodule commits [.gitmodules]' '
 '
 
 test_expect_success 'git diff (empty submodule dir)' '
-       : >empty &&
        rm -rf sub/* sub/.git &&
        git diff > actual.empty &&
-       test_cmp empty actual.empty
+       test_must_be_empty actual.empty
 '
 
 test_expect_success 'conflicted submodule setup' '