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kotlinlang

Why is it that this:

```    fun retrieveNavigationItem(context: Context, key: String) =
        ObjectInputStream(File(context.filesDir, key).inputStream()).readObject() as NavigationItem?```

Is perfectly accepted by the Kotlin compiler, but this:

```    fun &lt;T : Serializable&gt;retrieveSerializable(context: Context, key: String) =
            ObjectInputStream(File(context.filesDir, key).inputStream()).readObject() as T?```

Gives me a warning saying unchecked cast? Since `NavigationItem : Serializable` I don't understand the difference that would cause one to warn?