replace meeting.description with getattr(meeting, 'description', '')

To prevent:

Traceback (most recent call last):

 File "/usr/lib/pymodules/python2.6/django/core/handlers/base.py", line 92, in get_response
   response = callback(request, *callback_args, **callback_kwargs)

 File "/srv/summit.ubuntu.com/summit/schedule/decorators.py", line 51, in inner
   return func(request, summit, *args, **kwds)

 File "/srv/summit.ubuntu.com/summit/schedule/views.py", line 274, in ical
   response.write(schedule.as_ical())

 File "/srv/summit.ubuntu.com/summit/schedule/render.py", line 1122, in as_ical
   'roomname':room.name, 'description': meeting.description.replace('\r', '').replace('\n', '\N'),

AttributeError: 'NoneType' object has no attribute 'replace'