    def load_state(self, state):
        """Restore state about spawned single-user server after a hub restart.

        Local processes only need the process id.
        """
        super().load_state(state)
        if 'pid' in state:
            self.pid = state['pid']
Restore state about spawned single-user server after a hub restart.

Local processes only need the process id.
jupyterhub/spawner.py