t / t4013 / diff.diff_--no-index_--raw_--no-abbrev_dir2_diron commit filter-branch: fix errors caused by refs that point at non-committish (f78ab35)
   1$ git diff --no-index --raw --no-abbrev dir2 dir
   2:000000 100644 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 A      dir/sub
   3$