Another alternative would be to pass the Configuration through the newServerAggregator and they can individually choose to use it or not use it. This is fine for aggregators, because they're always created in the context of a coprocessor where we can get our hands on the Configuration. For expressions, this is harder, b/c they're not accessible for Filters. More of an aside, but it'd be nice to fix this and pass the Configuration to a Filter at construction time.