Deep merge and deep get on kotlin `Map<String,Any>` maps

DeepMaps.kt

import java.util.*
import kotlin.reflect.KClass

/**
 * Produces a new map that represents a merge of [source] into [this], returning an immutable view. Map leaves will be
 * overwritten from [source] into [this].
 *
 * @param source Nested [Map<String,Any>] that will be merged over [this]. Must be [Map<String,Any>]
 *
 * @throws IllegalArgumentException When [source] causes a [ClassCastException] caused by a non-[String] key
 */
fun Map<String, Any>.deepMerge(source: Map<String, Any>): Map<String, Any> =
  deepMerge(Stack<String>(), source)

fun Map<String, Any>.deepMerge(path: Stack<String>, source: Map<String, Any>): Map<String, Any> {
  return this.toMutableMap().let { destination ->
    try {
      for (key in source.keys) {
        if (source[key] is Map<*, *> && destination[key] is Map<*, *>) {
          @Suppress("UNCHECKED_CAST")
          destination[key] = (destination[key] as Map<String, Any>).deepMerge(
            path.also { it.push(key) },
            (source[key] as Map<String, Any>)
          )
        } else {
          destination[key] = source[key] as Any
        }
        path.clear()
      }
    } catch (e: ClassCastException) {
      throw IllegalArgumentException("Cannot deepMerge source['${if (path.empty()) "" else path.joinToString(".")}'] when keys are not Strings ...")
    }
    Collections.unmodifiableMap(destination)
  }
}

/**
 * Retrieves a value from a nested map using a dot-notated path.
 *
 * @param key Dot-notated path to the value retrieved
 *
 * @throws IllegalArgumentException When navigation fails because value is _null_ or we encounter a non
 *  [Map<String,Any>] entity in the path
 */
inline fun <reified R : Any> Map<String, Any>.deepGet(key: String): R =
  deepGet(Stack<String>().also { it.addAll(key.split(".").reversed()) }, key, R::class)

fun <R : Any> Map<String, Any>.deepGet(path: Stack<String>, key: String, type: KClass<R>): R {
  val current = path.pop()
  return if (path.empty()) {
    try {
      @Suppress("UNCHECKED_CAST")
      this[current] as R
    } catch (e: Exception) {
      val failedAt = key.split(".").dropLast(path.size).joinToString(".")
      throw IllegalArgumentException("Cannot deepGet key '$failedAt' as the value '${if (this[current] == null) "null" else this[current]!!::class.simpleName}' is not ${type.simpleName} ...")
    }
  } else {
    val remaining = this[current]
    if (remaining !is Map<*, *>) {
      val failedAt = key.split(".").dropLast(path.size).joinToString(".")
      throw IllegalArgumentException("Cannot deepGet key '$failedAt' as the value '${if (remaining == null) "null" else remaining::class.simpleName}' is not Map<String,Any> ...")
    }
    @Suppress("UNCHECKED_CAST")
    (remaining as Map<String, Any>).deepGet(path, key, type)
  }
}