ClassCastException when upgrading SDK from 28 to 29

Question

I have this bizarre problem with this function. When I target SDK 28, no problem and no crash happen. Here's the working code with target SDK 28.

  override fun getChildList(): List<Any> {
        val itemsWithSubCats: MutableList<in Any> = ArrayList(items)
        if (subCategories?.isNotEmpty() == true) {
            itemsWithSubCats.add(ArrayList<Any>(subCategories))
        }
        return itemsWithSubCats.toList() as List<Any>
    }

I've uploaded a release build to Playstore and I got an upgrade SDK problem. So I upgraded to 29 SDK, which causes compile error with the previous function, so I fixed it to the following one:

override fun getChildList(): List<Any> {
    val itemsWithSubCats: MutableList<in Any?> = mutableListOf(items)
    if (subCategories?.isNotEmpty() == true) {
        itemsWithSubCats.add(ArrayList<Any>(subCategories!!))
    }
    return itemsWithSubCats.filterNotNull().toList()
}

which causes a ClassCastException as follow:

java.lang.ClassCastException: java.util.ArrayList cannot be cast to ..RestaurantDetailsMenuItem

Answer 1

Assumpsions

items = arrayOf("a", "b")
subCategories = arrayOf("c", "d")

If you want to achieve itemsWithSubCats = listOf("a", "b", "c", "d"), then the code should be like:

val itemsWithSubCats: MutableList<in Any?> = items.toMutableList()
if (subCategories?.isNotEmpty() == true) {
   itemsWithSubCats.addAll(subCategories!!)
}
val list = itemsWithSubCats.filterNotNull().toList()

If you want to achieve itemsWithSubCats = listOf(arrayOf("a", "b"), arrayOf("c", "d")), then the code should be like:

val itemsWithSubCats: MutableList<in Any?> = mutableListOf(items)
if (subCategories?.isNotEmpty() == true) {
    itemsWithSubCats.add(subCategories!!)
}
val list = itemsWithSubCats.filterNotNull().toList()

In Android Studio, line

itemsWithSubCats.add(ArrayList<Any>(subCategories!!))

is clearly giving error on my side.