FragmentWithBundle.kt

class MainActivity : AppCompatActivity() {
	
  val bundle = Bundle().apply {
    putString(MainFragment.KEY_TEXT, "Now this won't crash")
  }
  val mainFragment = MainFragment().apply {
    arguements = bundle
  }
	
  override fun onCreate(savedInstanceState: Bundle?) {
    // the usual stuff
    if(savedInstanceState == null) {
    	supportFragmentManager.beginTransaction()
	    .add(R.layout.fragmentContainerView, mainFragment)
	    .commit()	
    	}	
    }
}

class MainFragment : Fragment() {
   lateinit var textToDisplay: String
  
   override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
     textToDisplay = requireArguments().getString(KEY_TEXT)
     // Logic related to using $textToDisplay
   }
  companion object {
    const val KEY_TEXT = "KeyText"
  }
}

Yes, thank you Gabor, I've updated the gist.