The (!!) operator

Instead of a null value, the !! operator will throw an NPE:

val result: String = nullableCupcake!!.eat()

If you can deal with an NPE, the !! operator gives you a pretty convenient feature, a free smart cast:

val result: String = nullableCupcake!!.eat()

val length: Int = nullableCupcake.eat().length

If nullableCupcake!!.eat() doesn't throw an NPE, Kotlin will change its type from Cupcake? to Cupcake from the next line and onwards.