AJAX Throbber - Keep throbber image but delete Please wait... message? This question has been asked a few times in various forms but is there a simple way to keep the animated blue throbbing image but delete the Please wait... text?

I'm trying this in my form_alter hook:

unset($form['my-model']['#ajax']['progress']['message']);
// or
$form['my-model']['#ajax']['progress']['message'] = '';


But this appears to remove the message AND the animated throbber! I want the throbber to remain. Is it a requirement for message to not be empty for the throbber to even render?
@Jimajamma answered the question correctly in the first comment. 

 $form['my-model']['#ajax']['progress']['type'] = 'throbber';
 $form['my-model']['#ajax']['progress']['message'] = NULL;


Must explicitly be set and configured within the ['#ajax'] form element.