IssueTracker

Component used: Navigation
Version used: 1.0.0
Devices/Android versions reproduced on: Google Pixel, Android 9

Suppose you have a nav graph like this for a fragment MyFragment.kt
```
<fragment>
    ...
    <argument
            android:name="anArg"
            app:argType="string"
            app:nullable="true"
            android:defaultValue="@null"/>
</fragment>
```

In MyFragment.kt, get nav args like this:

```
class MyFragment: Fragment {
   private val myArgs: MyFragmentArgs by navArgs()
}
```

When this fragment is started without any arguments (such as from a BottomNavView) then:
Expected Behaviour: `myArgs` is a bundle, where `myArgs.anArg` is null
Actual Behaviour: `myArgs` is null.

What's worse is that the `navArgs()` delegate function throw an exception and crashes the app if the given arguments bundle is null.

Actual code and screen recording can be found on this Github issue:
https://github.com/fossasia/open-event-android/issues/1242