[Bug Report] el-cascader 手动清空 options (设置为空数组) 时报错 ==> 机翻: el-cascader error when manually clearing options (set to empty array)

### Element UI version
2.15.7

### OS/Browsers version
Windows 10; Chorme v100.0

### Vue version
2.6.14

### Reproduction Link
https://codepen.io/dovahkinn/pen/YzYgxBR?editors=1111

### Steps to reproduce
1. codepen 加载完成, el-cascader 选择任意一项
2. 点击按钮
3. 控制台报错:
"[Vue warn]: Error in callback for watcher 'options': 'TypeError: Cannot read properties of null (reading 'level')'

found in

---> at packages/cascader-panel/src/cascader-panel.vue

### What is Expected?
手动将 options 置空时控制台无错误警告

### What is actually happening?
实际操作没有影响, 但是控制台报错