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

fun main(args: Array<String>) {
var computer="SCISSORS"

val default = "ROCK"

var rNumber=(1..3).random()

if(rNumber==1)
computer="ROCK"
else if(rNumber==2)
computer="PAPER"

println("\nEnter Your Choice: ROCK,PAPER,or,SCISSORS")
// use null safe ? and elvis operator ?: to provide default if nothing is entered
var player = readLine()?.uppercase()?:default
//check if user entered valid string
if(player !in
arrayOf("ROCK","PAPER","SCISSORS"))
player = default

print("\nPlayer ${player}\nComputer ${computer}\n\n")

if(computer==player)
println("it's Draw *----*")
else if(
computer=="ROCK" && player=="SCISSORS" ||
computer=="PAPER" && player=="ROCK" ||
computer=="SCISSORS" && player=="PAPER"
)
println("You Lost -_-")
else
println("You Won :)")

}