Kotlin extension
fun <T> DocumentSnapshot.getList(field: String): List<T>? { @Suppress("UNCHECKED_CAST") return get(field) as? List<T>}fun <T1, T2> DocumentSnapshot.getMap(field: String): Map<T1, T2>? { @Suppress("UNCHECKED_CAST") return get(UserQuoteHistory.QUOTES) as? Map<T1, T2>}NOTE: Refer to Kotlin Cast Any to List or Map: Unchecked Cast.
Usage
val items = doc.getList("items")