[Bug Report] 请问 我同end-date 的时候绑定的是@on-change方法，为何会报错

### VUX version
2.9.2

### OS/Browsers version
win7 64位

### Vue version
2.5.17

### Code

```html

data(){
Tday:''"
}

setToday(){ //获取当前日期并修改日期样式
let dayN = new Date() //创建日期对象
let year = dayN.getFullYear()
let mon = dayN.getMonth()
if(mon < 10){
mon = '0' (mon 1)
}
let day = dayN.getDate()
if(day < 10){
day = '0' day
}
let Tday = year '-' mon '-' day
this.Tday = Tday
console.log(Tday)
}
当我点击选择的时候，提示报错
Uncaught TypeError: Cannot read property 'style' of null
at eval (datetimepicker.js?74b6:192)

```

### Steps to reproduce
1.显示原代码
2.data 里初始化数据
3.绑定 Tday方法 并自己计算当前日期并修改日期格式

### What is Expected?
期待回复或修改

### What is actually happening?
..