Prevent type exception on concatenation if diffstat returns None. This will most often occur if diffstat is not installed in the target platform, though may also happen in other cases where diffstat fails to execute. Signed-off-by: Sean Dague <sean@dague.net>

#!/bin/sh

set -e

mkdir test
cd test
echo foo>foo
hg init
hg addremove
hg commit -m "1"
hg verify

hg clone . ../branch
cd ../branch
hg co
echo bar>>foo
hg commit -m "2"

cd ../test
hg pull ../branch
hg verify
hg co
cat foo
hg manifest --debug