`CompositeValueProvider` does not match `IBindingSourceValueProvider` contract

[dougbu]

Of the IBindingSourceValueProvider implementations in MVC, all but CompositeValueProvider have a Filter() method that returns null when the requested BindingSource does not match. CompositeValueProvider instead returns an empty CompositeValueProvider.

Also have a little code in CompositeModelBinder and MutableObjectModelBinder that expects the CompositeValueProvider behaviour of all IBindingSourceValueProvider impelmentations. That is, they need to change slightly to handle the expected / contracted null return values from Filter().

[Eilon]

Make 'em match!

[dougbu]

Teal it is 😈

[dougbu]

4a81377