t / t4101 / diff.0-2on commit receive-pack: don't pass non-existent refs to post-{receive,update} hooks (160b81e)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,2 +1,2 @@
   4 a
   5-b
   6+b
   7\ No newline at end of file