Inspiration: null safety in Kotlin

In Kotlin, null pointer exceptions are detected and eliminated at compile time. The type system distinguishes between references that can hold null and those that can not.

var a: String = null // compilation error
var b: String? = null // ok

. operator can be used to dereference non-nullable variable only:

val l = a.length // ok
val l = b.length // compile-time error: variable 'b' can be null

Safe calls ?. operator can be used to dereference nullable variable:

val l = b?.length
val l: Int? = if (b != null) b.length else null

Elvis operator ?: can be used to replace null-evaluated expression with non-null value:

val l = b?.length ?: -1
val l: Int = if (b != null) b.length else -1

More on null-safety in Kotlin: https://kotlinlang.org/docs/reference/null-safety.html