Android Material Button Toggle Group - Check None Selected

I am using MaterialButtonToggleGroup with single selection (only one button checked at a time). How to check if none of the buttons is checked?

        toggleGroup?.addOnButtonCheckedListener { group, checkedId, isChecked ->
        if (isChecked) {
            when (checkedId) {
                R.id.first_materialButton -> {
                    // do something when selected
                }

                R.id.second_materialButton -> {
                    // do something when selected
                }
            }
        }
    }

The solution would be to get the checkedButtonId from the group on the else branch for isChecked, and if it the value is -1, then no button is selected.

toggleGroup?.addOnButtonCheckedListener { group, checkedId, isChecked ->
    if (isChecked) {
        when (checkedId) {
            R.id.first_materialButton -> {
                // do something when selected
            }

            R.id.second_materialButton -> {
                // do something when selected
            }
        }
    } else {
        if (group.checkedButtonId == View.NO_ID) {
           // do something when nothing selected
        }
    }
}