I have a tracker that was upgraded from 0.6.5 to 0.7.8
to 0.8.2.

The old issues do not have an actor assigned.

In 0.7.8, the issue details show:

Created on 2004-04-27.13:10:37 by knittelc, last
changed 2004-04-30.17:03:15 by .

In 0.8.2, the issue details show:

Created on 2004-04-27.13:10:37 by knittelc, last
changed 2004-04-30.17:03:15 by [Attempt to look up
__render_with_namespace__ on a missing value].

Logged In: NO 

Same problem here on issue creation, quick and dirty fix:

/usr/lib/python2.3/site-packages/roundup #diff -s
cgi/templating.py.orig cgi/templating.py
1571c1571
<             msg = self._('Attempt to look up %(attr)s on a
missing value')
---
>             msg = self._('None')