NullableImmutable.kt

//So now after letting IntelliJ convert our file to Kotlin we get this:
//... but there's an error

class ExampleActivity : AppCompatActivity() {

    private var foo: String? = "Bar"

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        foo = something

        if (foo != null) {
            doSomething(foo) 
            //Smart cast to 'String' is impossible, 
            // because 'foo' is a mutable property that could have been changed by this time

        }
    }
}

//In order for our call to 'doSomething' to actually be guaranteed to work we need foo to be Immutable AND Non-null