code: def handle_got_features_event(self, event):
          
          server_features = set()
          logger.debug("Checking roster-related features")
          if event.features.find(FEATURE_ROSTERVER) is not None:
              logger.debug("  Roster versioning available")
              server_features.add("versioning")
          if event.features.find(FEATURE_APPROVALS) is not None:
              logger.debug("  Subscription pre-approvals available")
              server_features.add("pre-approvals")
          self.server_features = server_features
docs: Check for roster related features in the stream features received
          and set `server_features` accordingly.