Nullability in Kotlin Generic Extension Function Receivers

Nullable Kotlin GEF Receivers

fun main(args: Array<String>) {

    val nonnNullStr = "Str-"
    val nullStr: String? = null

    println(nonnNullStr.nullableConcat("1"))
    println(nullStr.nullableConcat("2"))

    println(nonnNullStr.nonnullableConcat("3"))
    // Why is this legal?
    println(nullStr.nonnullableConcat("4"))
}

fun <T> T?.nullableConcat(b: T) = this.toString() + b.toString()

fun <T> T.nonnullableConcat(b: T) = this.toString() + b.toString()