Kotlin Map Add if Not Found: getOrPut

class Batch(val id: String, val filenames: MutableList<String>)val batchId = ...val batches = mutableMapOf<String, Batch>()val batch = batches.getOrPut(batchId, {    Batch(id = batchId, filenames = mutableListOf())})batch.filenames.add("...")

val batch = batches[batchId] ?: let {    val b = Batch(id = batchId, filenames = mutableListOf())    batches[batchId] = b    b}