code: def _to_pb(self):
          
          client = self._instance._client
          location = client.instance_admin_client.location_path(
              client.project, self.location_id
          )
          cluster_pb = instance_pb2.Cluster(
              location=location,
              serve_nodes=self.serve_nodes,
              default_storage_type=self.default_storage_type,
          )
          return cluster_pb
docs: Create cluster proto buff message for API calls