Android GoogleSignIn.GetLastSignedAccount在GoogleSignIn.requestPermissions之后返回null

我用

请求额外权限，但在我重新启动应用程序GoogleSignIn.getLastSignedInAccount（上下文）后返回null

fun requestAdditionalPermission(activity: FragmentActivity) {
        if (!GoogleSignIn.hasPermissions(
                GoogleSignIn.getLastSignedInAccount(activity),
                Scope(DriveScopes.DRIVE_APPDATA))) {
            GoogleSignIn.requestPermissions(
                activity,
                REQUEST_APP_DATA_PERMISSION_REQUEST_CODE,
                GoogleSignIn.getLastSignedInAccount(activity),
                Scope(DriveScopes.DRIVE_APPDATA))
        }
    }