Convert text to morse code in Kotlin

TextToMorse.kt

/*
Write a function to convert a string given by the user, to the respective morse code sequence.

Morse code https://en.wikipedia.org/wiki/Morse_code

Example: 
User Input: Hello
Output: .... . .-.. .-.. ---
*/

fun main(args: Array<String>) {
    textToMorse("Hello")
}

fun textToMorse(s: String) : String {
    val morseArr = s.map{value -> convertCharToMorse(value)}
    println(morseArr.joinToString(" "))

    return s
}

fun convertCharToMorse(c : Char) = when (c.toLowerCase()) {
    'a' -> ".-"
    'b' -> "-..."
    'c' -> "-.-."
    'd' -> "-.."
    'e' -> "."
    'f' -> "..-."
    'g' -> "--."
    'h' -> "...."
    'i' -> ".."
    'j' -> ".---"
    'k' -> "-.-"
    'l' -> ".-.."
    'm' -> "--"
    'n' -> "-."
    'o' -> "---"
    'p' -> ".--."
    'q' -> "--.-"
    'r' -> ".-."
    's' -> "..."
    't' -> "-"
    'u' -> "..-"
    'v' -> "...-"
    'w' -> ".--"
    'x' -> "-..-"
    'y' -> "-.--"
    'z' -> "--.."
    '1' -> ".----"
    '2' -> "..---"
    '3' -> "...--"
    '4' -> "....-"
    '5' -> "....."
    '6' -> "-...."
    '7' -> "--..."
    '8' -> "---.."
    '9' -> "----."
    '0' -> "-----"
    else -> throw IllegalArgumentException("Not all characters are valid")
}