title: convert kotlin/java set to scala immutable
body: <p>Id like to convert an existing kotlin/java set, to scala immutable set, using kotlin/java code.</p>
  <p>scala.collection.JavaConversions.asScalaSet only gives me the mutable set.</p>
  <p>Must do it that way, because I am inheriting from a scala class on another repo, and would not like to insert scala packages and plugins to my project.</p>