push parameter instantiation to one method

actionpack/lib/action_controller/test_case.rb

@@ -457,6 +457,7 @@ def paramify_values(hash_or_array_or_value)
           hash_or_array_or_value.map {|i| paramify_values(i)}
         when Rack::Test::UploadedFile, ActionDispatch::Http::UploadedFile
           hash_or_array_or_value
+        when nil then {}
         else
           hash_or_array_or_value.to_param
         end
@@ -489,7 +490,6 @@ def process(action, http_method = 'GET', *args)
 
         @request.env['REQUEST_METHOD'] = http_method
 
-        parameters ||= {}
         controller_class_name = @controller.class.anonymous? ?
           "anonymous" :
           @controller.class.name.underscore.sub(/_controller$/, '')