message: vdom: fix null children
diff: @@ -78,12 +78,14 @@ function update(element: Element, node: VNode, isSvg: boolean) {
  element.parentNode.replaceChild(create(node, isSvg), element);
  } else {
  updateProps(element, node.props, isSvg);
  - node.children && updateChildren(element, node.children, isSvg);
  + updateChildren(element, node.children, isSvg);
  }
  }
  function updateChildren(element, children, isSvg: boolean) {
  - const len = Math.min(element.childNodes.length, children.length);
  + const old_len = element.childNodes?.length || 0;
  + const new_len = children?.length || 0;
  + const len = Math.min(old_len, new_len);
  for (let i = 0; i < len; i++) {
  const child = children[i];
  const el = element.childNodes[i];
  @@ -113,7 +115,7 @@ function updateChildren(element, children, isSvg: boolean) {
  n--;
  }
  - if (children.length > len) {
  + if (new_len > len) {
  const d = document.createDocumentFragment();
  for (let i = len; i < children.length; i++) {
  d.appendChild(create(children[i], isSvg));
  