获取鼠标左右键为undefined

Creator 3.x
#1

Creator 版本： 3.6.1

目标平台：模拟器

代码：

import { _decorator, Component, input, Input, EventMouse } from 'cc';
const { ccclass, property } = _decorator;

@ccclass('Index')
export class Index extends Component {
   start() {
       input.on(Input.EventType.MOUSE_UP, this.onMouseUp, this);
   }

   onMouseUp(event: EventMouse){
       console.log("mouse click :"+event.getButton());
   }

   update(deltaTime: number) {
       
   }
}
结果：mouse click :**undefined**