// Java:
Arrays.asList("a1", "a2", "a3")
    .stream()
    .findFirst()
    .ifPresent(System.out::println);

// Kotlin:
listOf("a1", "a2", "a3").firstOrNull()?.apply(::println)

or, create an extension function on String called ifPresent:

// Kotlin:
inline fun String?.ifPresent(thenDo: (String)->Unit) = this?.apply { thenDo(this) }

// now use the new extension function:
listOf("a1", "a2", "a3").firstOrNull().ifPresent(::println)

See also: [apply() function](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/apply.html)

See also: Extension Functions

See also: [?. Safe Call operator](https://kotlinlang.org/docs/reference/null-safety.html#safe-calls), and in general nullability: http://stackoverflow.com/questions/34498562/in-kotlin-what-is-the-idiomatic-way-to-deal-with-nullable-values-referencing-o/34498563#34498563