Why can I not add two numbers in Kotlin using this source code?
<p>This is the code I have created to add two numbers: </p>

<pre><code>import java.util.*

fun main(args: Array&lt;String&gt;) {
    val (a, u) = readLine()!!.split(' ').map(String::toInt)

    println(add(a, u))
}

fun  add(a: Int, u: Int) = a + u
</code></pre>

<p>However I keep getting this error : </p>

<pre><code>Exception in thread "main" java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:592)
    at java.lang.Integer.parseInt(Integer.java:615)
    at Kotlin_learnKt.main(kotlin^learn.kt:6)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Process finished with exit code 1
</code></pre>

<p>I am not sure what I am doing wrong. I just want to be able to prompt the user to enter two numbers, have the code add them, then return the result. </p>