Graph API调用中EmployeeHireDate字段返回NULL的问题求助

我现在在用C#调用Graph API，代码如下：

var result = await graphClient.Users["{myID}"].GetAsync((requestConfiguration) => {
    requestConfiguration.QueryParameters.Select = new string []{ "displayName","givenName","postalCode","id","EmployeeHireDate" };
});

我能获取到查询里提到的其他所有属性，但EmployeeHireDate一直返回NULL，有没有大佬能给我支个招解决这个问题呀？

内容来源于stack exchange