How do I make TrieMap serializable in Scala?

I know how to serialize a class like this:

@SerialVersionUID(42L)
class foo extends Serializable {
    val bar = scala.collection.concurrent.TrieMap[Int, Map[String, Any]]()
}

      

        
        
        
      

    

But what if I just want to make the variable serializable, in this case simple bar

? How can I achieve this?