WARN：The string type is not recommended for date-picker, use "Date" type

[itning]

Reproduction link

https://stackblitz.com/edit/angular-bmvpiq?file=src/app/app.component.ts

Steps to reproduce

1. 选择日期和时间
2. 控制台出现警告：
   ng-zorro-antd-core-logger.js:26 [NG-ZORRO]: The string type is not recommended for date-picker, use "Date" type

What is expected?

希望是 null 或者 undefind的时候 不出现警告信息
即：

• date1:Date;
• date1:Date=undefind;
• date1:Date=null;

What is actually happening?

出现警告信息

Environment	Info
ng-zorro-antd	11.0.1
Browser	Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36 t: 1609679376999

[itning]

还有个问题就是
nzDefaultPickerValue 不起作用 设置了没用