I can't seem to find org.apache.lucene.facet.search.params.IFieldSet in Lucene 4.1.0 source even though the JAR from maven has it

I'm trying to migrate the Lucene jars for our product from 4.1.0 to the latest if possible. I noticed that we seem to be using org.apache.lucene.facet.search.params.IFieldSet derived classes for our facet searches but I don't see this in the source code.

Anybody have a clue as to what's happening here?

I've tried

• Re-downloading the maven jars to be sure, I dont see it.
  • UPDATE: Turns out the JAR is checked into the source tree and this particular one is not pulled from Maven
• Downloading the tar binaries from lucene archives, don't see it there
• Syncing the lucene source code to the tags/releases/lucene-solr/4.1.0 tag, still don't see it

A co worker remarked about the possibility of a fat jar but from what I understand they cannot have conflicting namespaces.

IFieldSet values are also returned from getFieldSet function in org.apache.lucene.facet.search.results.FacetResultNode, for the second and third above that does NOT have IFieldSet, there is also no getFieldSet function.

As @MatsLindh helpfully pointed out in the comment above, my company apparently has a custom version of the jar augmented by an employee in the past who built most of the original code.