text: from cartographer.serializers import JSONAPISerializer
  from cartographer.utils.version import JSONAPIVersion
  
  
  class JSONAPINullSerializer(JSONAPISerializer):
      def as_linkage_json(self):
          return None
  
      def as_link_json(self, version):
          if version == JSONAPIVersion.JSONAPI_RC2:
              return {"id": None}
          elif version == JSONAPIVersion.JSONAPI_RC3:
              return {"linkage": self.as_linkage_json()}
          elif version == JSONAPIVersion.JSONAPI_1_0:
              return {"data": self.as_linkage_json()}
          else:
              raise ValueError("Unknown JSON API version")
  