code: public List<WnsNotificationResponse> pushTile(List<String> channelUris, WnsTile tile) throws WnsException {
  		return this.pushTile(channelUris, null, tile);
  	}
docs: Pushes a tile to channelUris
  @param channelUris
  @param tile which should be built with {@link ar.com.fernandospr.wns.model.builders.WnsTileBuilder}
  @return WnsNotificationResponse please see response headers from <a href="http://msdn.microsoft.com/en-us/library/windows/apps/hh465435.aspx#send_notification_response">http://msdn.microsoft.com/en-us/library/windows/apps/hh465435.aspx#send_notification_response</a>
  @throws WnsException when authentication fails