What about: ``` fun MutableMap<String, Any>....

# codereview

[kingsley]

What about:

fun MutableMap<String, Any>.mergeWith(mapOverride: Map<String, Any>?) {
    mapOverride?.forEach { (k, v) ->
        val baseValue = this[k]
        this[k] = when {
            baseValue is Set<*> && v is Set<*> -> baseValue + v
            else -> v
        }
    }
}