old_contents: from flotype import serializer
  
  class Client(object):
      def __init__(self, bridge, id):
          self.bridge, self.clientId = bridge, id;
      def get_service(self, svc):
          return reference.Reference(self, ['client', id, svc])
  
new_contents: from flotype import serializer, reference
  
  class Client(object):
      def __init__(self, bridge, id):
          self.bridge, self.clientId = bridge, id;
      def get_service(self, svc):
          return reference.Reference(self, ['client', id, svc])
  
subject: Add missing import.