Update Immutable Map in Scala

updateMap.scala

def updateMap[A, B](map: Map[A, List[B]], key: A, value: B) =
        map + ((key, map.getOrElse(key, List()) ::: List(value)))

var topicsMap = offsetsRanges.map { o => (o.topic, List[String]())}.toMap
offsetsRanges.foreach { o => 
      topicsMap = updateMap[String, String](topicsMap, o.topic, (o.partition + ":" + o.untilOffset))}