gistfile1.txt

    private def shrinkDBO(dbo: DBObject): DBObject = {
        def isDBO(v: AnyRef) = v.isInstanceOf[DBObject]
        def isEmptyDBO(v: AnyRef) = isDBO(v) && v.asInstanceOf[DBObject].isEmpty
        def shrink(v: AnyRef) = if (isDBO(v)) shrinkDBO(v.asInstanceOf[DBObject]) else v

        dbo match {
            case _: BasicDBList =>
                val ls = new BasicDBList()
                (dbo.mapValues(shrink(_)).filter(!isEmptyDBO(_)).values).foreach(ls.add(_))
                ls
            case _ =>
                dbo.filter(e => e._1.length <= 3) // don't allow keys with more than 3 characters
                        .mapValues(v => shrink(v)) // recursively
                        .filter(e => !isEmptyDBO(e._2)) // finally: purge empty lists
        }
    }