in scala-repl/src/main/scala/org/jetbrains/ztools/scala/core/TrieMap.scala [92:95]
def put(key: Array[String], value: T): Option[TrieMap.Node[T]] = {
val node = subtree(key, key.length - 1)
node.put(key(key.length - 1), new TrieMap.Node[T](Option.apply(value)))
}