@Test
public void revisionId_should_return_null_in_empty_repo() throws IOException {

  worktree = temp.newFolder().toPath();
  Repository repo = FileRepositoryBuilder.create(worktree.resolve(".git").toFile());
  repo.create();
  git = new Git(repo);
  Path projectDir = worktree.resolve("project");
  Files.createDirectory(projectDir);
  GitScmProvider provider = newGitScmProvider();
  assertThat(provider.revisionId(projectDir)).isNull();
}