If i got view which inherits from:
System.Web.Mvc.ViewPage
Where Foo has a property Bar with a type string
And view wants
If you pass null as the model to RenderPartial, then it will look at the original model, which is why the error says foo.
You'll need to make sure that bar is initialized to be an empty string instead of null.
Edit: @Arnis, look at the source code. It doesn't lie. You are passing null to the overload of RenderPartial. You are not passing Foo. Internally, the system uses the Model from your page's ViewContext (which is Foo) when you pass a null Bar to RenderPartial.