Example of migration from java Optional to Kotlin

optional.kt

// That's pretty much an implementation of singleton btw
object Optional {
    fun <T: Any> onNullable(obj: T?) : Iterable<T> {
        if (obj != null) {
            return listOf(obj)
        }
        return emptyList()
    }
}

fun parseAndIncKotlin(number: String?): Int {
    return Optional.onNullable(number)
            .map {
                Integer.parseInt(it)
            }.map {
                it + 1
            }.ifEmpty {
                listOf(0)
            }.first()
}