safe.md

``` kotlin /* Get rid of those pesky NullPointerExceptions, you know, The Billion Dollar Mistake */

var output: String output = null // Compilation error

// Kotlin protects you from mistakenly operating on nullable types

val name: String? = null // Nullable type println(name.length()) // Compilation error

// And if you check a type is right, the compiler will auto-cast it for you

fun calculateTotal(obj: Any) { if (obj is Invoice) obj.calculateTotal() }

</div>