Fix args to SearchFilters
Fix args to SearchFilters

Argument defaults should be None:

http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments

...and we aren't assuming the request argument is a dict.

mtekel/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend