Scala uJson code to censor certain field names

Censor.scala

import ujson.{ Obj, Value }

object Censor{ 

def updateAll(root: Value, target: (String => Boolean), newValue: Value): Value = {

    def update(value: Value, parent: Value = null, valueName: String = null): Unit = {
      value match {
        case Obj(values) =>
          values.map { case (name, v) => update(v, value, name) }
        case _ =>
          if (target(valueName)) parent(valueName) = newValue
      }
    }

    update(root)
    root
  }
}

example.scala

val raw=""" {
| "stuff" : {
| "password": [1,2,3]
| },
| "password" : "value1",
| "key2" : {
| "password" : 1233333,
| "key23" : [ "alpha", "beta", "gamma"],
| "key24" : {
| "password": true,
| "key242" : "value242",
| "confirmPassword": "dontshowthis"
| }
| }
|}""".stripMargin

val playjson: JsValue = Json.parse(raw)

//updateAll(json2,_=="password", "****cen***") // single field
updateAll(playjson,Set("password","confirmPassword"), "****cen***") // set, which is of course a predicate also

output.json

{
  "stuff": {
    "password": "****cen***"
  },
  "password": "****cen***",
  "key2": {
    "password": "****cen***",
    "key23": [
      "alpha",
      "beta",
      "gamma"
    ],
    "key24": {
      "password": "****cen***",
      "key242": "value242",
      "confirmPassword": "****cen***"
    }
  }
}