[Bug Report] /src/utils/ util.js In the isempty function verification in the file, when the value type is number, if the number value is 0?

### Element UI version
2.13.2

### OS/Browsers version
windows10/chorme

### Vue version
3.0.0-beta.14

### Reproduction Link
https://github.com/ElemeFE/element

### Steps to reproduce
/src/utils/util.js 文件中 isEmpty 函数校验中当值的类型是number时，如果number值为0？
源码：
if (typeof val === 'number') return !val;
如果val为0，就是一个bug

### What is Expected?
if (typeof val === 'number') return !val;
添加判断

### What is actually happening?
if (typeof val === 'number') return !val;
添加判断（嗯，应该是bug）