# get list of changed files
open my $fd, "-|", git_cmd(), "diff-tree", '-r', @diff_opts,
- $co{'parent'}, $co{'id'}, "--", (defined $file_name ? $file_name : ())
+ $co{'parent'} || "--root",
+ $co{'id'}, "--", (defined $file_name ? $file_name : ())
or next;
my @difftree = map { chomp; $_ } <$fd>;
close $fd