code: public static PushNotificationPayload sound(String sound) {
  		if (sound == null) throw new IllegalArgumentException("Sound name cannot be null");
  		PushNotificationPayload payload = complex();
  		try {
  			payload.addSound(sound);
  		} catch (JSONException e) {
  		}
  		return payload;
  	}
docs: Create a pre-defined payload with a sound name.
  
  @param sound the name of the sound
  @return a ready-to-send payload