kotline program showing "Unhandled Exception: Input string was not in a correct format."

Question

I don't know what's wrong with this code can anyone tell me why it's showing an error
code:
fun main(args: Array<String>) {
var ComputersChoice=""
var PlayerChoice=""
var RandomNumber=(1..3).random()
if(RandomNumber==1){
ComputersChoice="ROCK"
}else if(RandomNumber==2){
ComputersChoice="PAPER"
}else{
ComputersChoice="SCISSORS"
}
println("\nEnter Your Choice: ROCK,PAPER,or,SCISSORS")
PlayerChoice=readln().uppercase()
if(ComputersChoice==PlayerChoice)
{
println("it's Draw *----*")
}else if(ComputersChoice=="ROCK" && PlayerChoice=="SCISSORS" || ComputersChoice=="PAPER" && PlayerChoice=="ROCK" || ComputersChoice=="SCISSORS" && PlayerChoice=="PAPER"){
println("You Lost -_-")
}else{
println("You Won :)")
}

}

Answer 1

readLine() instead of readln()

Answer 2

Change your input line like this:

PlayerChoice=readLine()?.uppercase() ?: ""

Answer 3

Sololearn does not recognize readln.
Also, I added some more input validation
and single character input for user convenience.

https://sololearn.com/compiler-playground/cAzyMDR9CV4n/?ref=app