code: func (rn *registeredNode) checkSessionID(sessionID string) error {
  	rn.mu.Lock()
  	defer rn.mu.Unlock()
  
  	// Before each message send, we need to check the nodes sessionID hasn't
  	// changed. If it has, we will the stream and make the node
  	// re-register.
  	if sessionID == "" || rn.SessionID != sessionID {
  		return status.Errorf(codes.InvalidArgument, ErrSessionInvalid.Error())
  	}
  
  	return nil
  }
docs: // checkSessionID determines if the SessionID has changed and returns the
  // appropriate GRPC error code.
  //
  // This may not belong here in the future.