How to check for empty data source

I'm trying to show a different panel when the data set is empty using the following script in the data source on change event:    

if (DS_1.isResultSetEmpty())

{

  PANEL_ASSETS_NOT_FOUND.setVisible(true);

}

else

{

  PANEL_ASSETS_NOT_FOUND.setVisible(false);

}

However the data source is never empty. Yet, when I apply filters to the data set the chart control displays the "No data found" message.

The first time the dashboard loads up there is data in DS_1. When filters are applied there is no data in DS_1.

I've tried using .getMembers and .getDeminsions and they are arrays with length greater then zero.

If I am unable to use the isResultSetEmpty() method on the data source?

Thanks for your help,

Pete