在Scala中，如何将嵌套了HashMap的嵌套HashMap转换为json？

libraryDependencies += "com.typesafe.play" %% "play-json" % "2.9.2"

import play.api.libs.json._

val nestedMap: Map[String, Map[String, String]] = Map(
  "key1" -> Map("nestedKey1" -> "value1", "nestedKey2" -> "value2"),
  "key2" -> Map("nestedKey3" -> "value3", "nestedKey4" -> "value4")
)

val json: JsValue = Json.toJson(nestedMap)

println(Json.prettyPrint(json))