>Maybe I'm misunderstanding your problem. If you create a client HttpWebRequest then you can just set its UserAgent property to whatever you wish.

Yes, but that is only an exception. The reference to HttpWebRequest was for a custom client that is calling the framework. The framework, on the server side, is responsible for much more than that. So, it has to be kept generic. I also want to cover the possibility, that even if I would define a user agent on the client side, that others can do the same and not pass it. In that case, I really need to verify for its nothing object.