flexible overlay 添加backdropClick时报错

### Version

latest

### Vue Version

3

### Link to minimal reproduction

http://localhost:3000/components/overlay/#%E5%BC%B9%E6%80%A7%E9%81%AE%E7%BD%A9%E5%B1%82

### Step to reproduce

点击显示按钮， 然后再点击背景控制台报错

### What is expected

_No response_

### What is actually happening

_No response_

### Any additional comments (optional)

_No response_