Add a new collection and interface for the filter options. Now it is possible to add filter options as key => value pair to the collection.
Implement a new function in the interface and data provider. This new function creates a empty filter option collection.
Change the return value from all "getFilterOptions" functions from a CollectionInterface to a FilterOptionCollectionInterface. Change a call in the function "getFilterOption" from "getEmptyCollection" to "getEmptyFilterOptionCollection".
Change the jandling from the filter options based on the new "FilterOptionCollectionInterface".
Improvement, all empty collection will be createt by the function "getEmptyCollection()" and not directly by a "new DefaultCollection();" call.