排除ActionFilterAttribute中的“值“null”对…无效”

在webapi项目中,我们有这样一个模型:

public class Person
{
    public string Name { get; set; }

    public Guid? Id { get; set; }
}

public class ModelActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        (...)
        var modelState = actionContext.ModelState;
        if (modelState.IsValid == false)
        {
            actionContext.Response = actionContext.Request.CreateErrorResponse(HttpStatusCode.BadRequest, modelState);
        }

        base.OnActionExecuting(actionContext);
    }
}

问题是,打这样的电话: https://localhost/person?Id=null&name= “John”会创建以下错误:

The value 'null' is not valid for Id.

我可以遍历错误列表并排除这一个,但感觉真的错了。