code: func (r *rootRotationReconciler) UpdateNode(node *api.Node) {
  	r.mu.Lock()
  	defer r.mu.Unlock()
  	// if we're not in the middle of a root rotation ignore the update
  	if r.currentRootCA == nil || r.currentRootCA.RootRotation == nil {
  		return
  	}
  	if hasIssuer(node, &r.currentIssuer) {
  		delete(r.unconvergedNodes, node.ID)
  	} else {
  		r.unconvergedNodes[node.ID] = node
  	}
  }
docs: // assumption:  UpdateNode will never be called with a `nil` node because the caller will be acting in response to
  // a store update event