gistfile1.txt

data class IBAN(val country: String, val account : String)

// parseIBAN returns nullable IBAN
fun parseIBAN(code : String) : IBAN? {
 ...
}

val iban = parseIBAN(userInput)
when (iban) {
  null -> throw InvalidIBANException()
  else -> when(iban.country) { // iban here is already of type IBAN, not nullable
    "DE" -> ...
    "IT" -> ...
    else -> ... all other countries
  }
}