Currently, if you want to have a property which is not of type "content", "user" or "boolean", your property has to be enumerated.

To write the facet, you have to implement getEnumerator() or to set an enumerator on configuration with method setEnumerator().

But to read the facet, you also have to implement getCriterionEnumerator() because Property interface has a default implementation returning null (which override (with no reason) default implementation from ElementDefinition which calling getEnumerator()).
This enumerator should supports the old API because it is like this in AbstractSearchUICriterion.configureEnumerator(...).

Also, we should have a simply enumerator which only manage the self value to make a property easily facetable.