setup使用getCurrentInstance()返回的对象是null

[seafronthu]

setup() {
    alert(1);   // 弹了两次
    const  instance = getCurrentInstance();
    console.log(instance)  // 结果是null 
    // do something
    return {}
}

@vue/composition-api版本：1.7.0 （还原到1.4.4正常）
vue版本：2.6.11

[Anthony Fu]

We temporarily close this due to the lack of enough information.
Please provide a minimal reproduction to reopen the issue.
Thanks.

Why reproduction is required