setOfNotNull

Returns a new read-only set either with single given element, if it is not null, or empty set if the element is null. The returned set is serializable (JVM).

fun <T : Any> setOfNotNull(element: T?): Set<T>(source)(source)

fun main() {
    val nonEmptySet = setOfNotNull("Kotlin")
    val emptySet = setOfNotNull<String>(null)

    println(nonEmptySet) // [Kotlin]
    println(emptySet)    // []
}

Source