format-patch on permission change gives empty patch

From: David Miller <davem@davemloft.net>
Date: Oct 7, 2010, 00:37 UTC
Message-ID: <20101006.173714.245380201.davem@davemloft.net>

When I ask git to format-patch a commit that is just a file permission change, it ends up generating an empty file, not even the commit message is included.

davem@sunset:~/src/GIT/net-2.6$ git show
commit a5dbc62ed61bf4cc57e22b78e5794880f1c74b90
Author: Joe Perches <joe@perches.com>
Date:   Wed Oct 6 17:32:49 2010 -0700

    Documentation/networking/ixgbevf.txt: Change file permissions to 644
    
    Signed-off-by: Joe Perches <joe@perches.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
You have new mail in /var/mail/davem
davem@sunset:~/src/GIT/net-2.6$ git format-patch HEAD^
0001-Documentation-networking-ixgbevf.txt-Change-file-per.patch
davem@sunset:~/src/GIT/net-2.6$ ls -l 0001-Documentation-networking-ixgbevf.txt-Change-file-per.patch 
-rw-r--r-- 1 davem davem 0 Oct  6 17:36 0001-Documentation-networking-ixgbevf.txt-Change-file-per.patch
davem@sunset:~/src/GIT/net-2.6$ git version
git version 1.7.3.1