code: def json_data(self, instance, default=None):
          
          value = self.get(instance)
  
          out = []
          for rel in value:
              if rel.isBroken():
                  logger.warn("Skipping broken relation {}".format(repr(rel)))
                  continue
              obj = rel.to_object
              out.append(api.get_url_info(obj))
          return out
docs: Get a JSON compatible value