Using the new save() in the file reference class

For a project I am working on, I allow users to drag stuff around the stage and then let them save it as JPEG. I have used the new save method from player 10. This is my code so far.

var fr:FileReference;

test_btn.addEventListener(MouseEvent.CLICK, showPic);

function showPic(event:MouseEvent):void {

var bmd:BitmapData=new BitmapData(970,570);
import com.adobe.images.JPGEncoder;

var jpgEncoder:JPGEncoder=new JPGEncoder(85);
var jpgStream:ByteArray=jpgEncoder.encode(bmd);;


But when I click on the button, I get the following erro

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at homev1_fla::MainTimeline/showPic()

What am I doing wrong, please help!