IssueTracker

You don't need to do step 1 or 2 - ensuring you've called addNavigator() before setGraph() is enough.

Specifically, see https://issuetracker.google.com/issues/110763345#comment2

Also mentioned is the fact that you can override createFragmentNavigator(), call navController.navigatorProvider.addNavigator() there, then return super.createFragmentNavigator().

It's may also be of interest that I am making use of a custom navigator to implement conditional routing.  My custom destination/nodes simply implement an interface like this:  
interface DynamicNode {
    @IdRes
    fun getDestination(context: Context, @IdRes destinationIn: Int, argsIn: Bundle?) : Int
}

The Navigator then implements a navigate method that simply calls NavController.navigate using the ID returned by the DynamicNode and returns null, essentially performing a redirect.  It would be cool to see something like this baked-in with a later version of the Navigation component.