convert: Using --dest-type svn crashed, if the source repo used tags.
The convert extension requires puttags(self, tags) to return a sequence
for a multi-variable assignment. If puttags implicitly returns None,
the code will break when trying to un-pack None for assignment.
#!/bin/sh
# http://mercurial.selenic.com/bts/issue433
hg init a
cd a
echo a > a
hg commit -Ama
hg parents -r 0 doesnotexist
true