When the onload callback does not add children, the tree component throws an exception

[ZerroRt]

TuSimple/naive-ui version (版本)

2.16.0

Vue version (Vue 版本)

3.2.0-beta.7

Browser and its version (浏览器及其版本)

Microsoft Edge(92.0.902.62)

System and its version (系统及其版本)

Windows Feature Experience Pack 421.18901.0.3

Node version (Node 版本)

Reappearance link (重现链接)

https://codesandbox.io/s/nervous-meadow-dw77n?file=/src/Demo.vue

Reappearance steps (重现步骤)

In the onload callback, children are not added to the current node but directly return Promise.resolve()

Expected results (期望的结果)

The node is folded again, and when it is clicked again to try to open, try to trigger the reload logic again

Actual results (实际的结果)

Throw an error "Cannot read property'forEach' of undefined" (in sandbox) or the node is stuck in the loading state

Remarks (补充说明)

[07akioni]

It's caused by expanding logic.