Oops…

Trac detected an internal error:
AttributeError: 'NoneType' object has no attribute 'id'

There was an internal error in Trac. It is recommended that you notify your local Trac administrator with the information needed to reproduce the issue.

To that end, you could a ticket.

The action that triggered the error was:

GET: /discussion/topic/34

TracGuide — The Trac User and Administration Guide