How to check if ViewBag has a certain dynamically created property or not?

[kender]

Folks,

Suppsoe that a certain dynamic property of a ViewBag object is optional. How can I check whether it has been created or not?
My first reaction is to check for null value.

@if (ViewBag.OptProp != null) {...}

But then how to handle the case when the property has been actually created, but the value assigned to it is null ?

Any suggestion, insight or reference is really appreciated!

Cheers,
- Nick

p.s. I think, my question is similar to this one: How do I check if an object has a property in JavaScript?. Except mine is about .NET .