See https://code.djangoproject.com/ticket/18450 for details
Although I'm not sure why right now, I wonder if the 'default' filter is there for a reason. Why do you think it's safe for it to be removed?
Cause newstyle urlresolving should always work nowadays. I think this is from the time where we had to support old admin urls which where just relative and the namespace refactor.
Fixed #139 -- Replaced all tabs in templates with two spaces.
git grep -Il ' ' -- templates | xargs sed -i 's/ / /g'