checkNotNull

Throws an IllegalStateException if the value is null. Otherwise returns the not null value.

@IgnorableReturnValueinline fun <T : Any> checkNotNull(value: T?): T(source)

fun main() {
    val nullableName: String? = "Kotlin"
    val name: String = checkNotNull(nullableName)  // throws IllegalStateException if null
    println("Name length: ${name.length}")
}

Source