Component used: Navigation
Version used: 2.0.0
Devices/Android versions reproduced on: during development; any IDE
SDK: Java

Summary:
I can't unit test any production code that tries navigating to an auto-generated Action class that has a default value. It seems (in version 2.0.0) that the default values are set by the NavController instead of baked into the auto-generated class. The result is that I get some NullPointerExceptions when trying to unit test navigation.

To reproduce:
1. In nav graph xml, add an argument having a default value to an action
<fragment
android:id="@id/screen1_fragment"
android:name="com.yourapp.yourpackage.Screen1Fragment"
<action
android:id="@+id/action_screen1_to_screen2"
app:destination="@id/screen2_fragment"
<argument
android:name="myBoolean"
app:argType="boolean"
android:defaultValue="false" />
</action>
</fragment>

2. In prod code, navigate using this action without overriding the default
NavController.navigate(Screen1FragmentDirections.actionScreen1ToScreen2());

3. In a unit test, try to verify that the screen1-to-screen2 navigation was invoked
verify(NavController).navigate(Screen1FragmentDirections.actionScreen1ToScreen2());

Expected: Unit test passes with flying colors

Actual: NullPointerException is thrown when the verify() does an equals() comparison. The auto-generated class does not contain default values, and so ActionScreen1ToScreen2.getMyBoolean() method attempts to cast a null value into a boolean, like so:

public boolean getMyBoolean() {
return (boolean) arguments.get("myBoolean");
}

Seems like a testability issue. If there's something I'm missing please let me know.

Related Issues (but not the same):
* SafeArg Builder classes doesn't contain the default values (https://partnerissuetracker.corp.google.com/issues/140123727)