When Select A Title, That Title Should Be Returned To Model?

In my application I have the following message:Object reference not set to an instance of an object.

@Html.DropDownList("Title",ViewData["PersonTitle"] as SelectList, Model.Person.Title)

The dropdownlist contains simple strings (person titles). When you select a title, that title should be returned to my model. Controller code:

ViewData["PersonTitle"] = new SelectList(new[] { "Dhr.", "Mevr." });

Why is this not working ? Edit: The purpose is to change

@Html.EditorFor(model => model.Person.Title)

into something like this

@Html.DropDownList("Title",ViewData["PersonTitle"] as SelectList, Model.Person.Title)