docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'url') and self.url is not None:
              _dict['url'] = self.url
          if hasattr(self, 'limit_to_starting_hosts'
                    ) and self.limit_to_starting_hosts is not None:
              _dict['limit_to_starting_hosts'] = self.limit_to_starting_hosts
          if hasattr(self, 'crawl_speed') and self.crawl_speed is not None:
              _dict['crawl_speed'] = self.crawl_speed
          if hasattr(self, 'allow_untrusted_certificate'
                    ) and self.allow_untrusted_certificate is not None:
              _dict[
                  'allow_untrusted_certificate'] = self.allow_untrusted_certificate
          if hasattr(self, 'maximum_hops') and self.maximum_hops is not None:
              _dict['maximum_hops'] = self.maximum_hops
          if hasattr(self,
                     'request_timeout') and self.request_timeout is not None:
              _dict['request_timeout'] = self.request_timeout
          if hasattr(
                  self,
                  'override_robots_txt') and self.override_robots_txt is not None:
              _dict['override_robots_txt'] = self.override_robots_txt
          return _dict