ASP .NET Web API控制器动作的参数为null但ModelState.IsValid仍为true，为什么？

Question says it all, I have a Web API controller action, that takes a POCO. It's a POST action, and I'm intentionally not posting the parameter to the action, however the ModelState.IsValid property still shows true. Why would that be? Is there an attribute that I have to set on the controller action and its parameters to enforce the validation?Question says it all, I have a Web API controll