do not write null sha1s to on-disk index

diff --git a/RelNotes b/RelNotes
index 1126dfef4f19b583f54ec6fa7e4ef8db9badaf65..3f4ce9f4f14e45b9bb20577be8d63da79174cb4f 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.5.0.7.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.9.6.txt
\ No newline at end of file