Creating a simple union of two Maps where values in 'core' will be overwritten by the 'overlay' and values in overlay that do not exist in core will be added to the resulitng Map

mapUnion.scala

val key0 = ("0","0")
val key1 = ("1","0")
val key2 = ("2","0")
val key3 = ("3","0")
 
val core:Map[(String,String),Option[String]] = Map(key0 -> Some("a"), key1 -> Some("b"), key2 -> Some("c"))
val overlay:Map[(String,String),Option[String]] = Map(key2 -> Some("y"), key3 -> Some("z"))
 
//val expected = Map(key0 -> Some("a"), key1 -> Some("b"), key2 -> Some("y"), key3 -> Some("z"))
 
def bundle(core: Map[(String,String),Option[String]], overlay: Map[(String,String),Option[String]]) = {
//def bundle(core: Map[(String,String),Option[String]], overlay: Map[(String,String),Option[String]]): Map[(String,String),Option[String]] = {
  val coreKeySet = core.keySet
  val overlayKeySet = overlay.keySet
 
  val keys = coreKeySet.union(overlayKeySet)
 
  val mmap = keys.map { k =>
    if (overlayKeySet.contains(k))
      (k, overlay.get(k).get)
    else
      (k, core.get(k).get)
  }
  mmap.toMap
}
 
val foo = bundle(core,overlay)