TypeError: Error #2007: Parameter child must be non-null.

Hello,

I am new to actionscript 3.0, I have Adobe Flash Builder 4.7 installed and I am creating a ActionScript project (File -> New -> ActionScript Project) named as Test. As you know flash builder does not include fl.controls package by default. I have added this package to my project as source path or swc file so that I can use the default components (e.g. Buttons, RadioButtons, Checkboxes) and now I am writing the following code.

package

{

          import flash.display.Sprite;

          import fl.controls.Button;

          [SWF(width = "640", height = "480", frameRate = "60", backgroundColor = "#FFFFFF")]

          public class Test extends Sprite

          {

                         private var btn:Button;

       public function Test()

                    {

                              btn = new Button();

                              btn.label = "CLICK ME!";

                              btn.x = 100;

                              btn.y = 100;

               addChild(btn);

                    }

          }

}

I am creating a fl.controls.Button instance in Test class and trying to add it on stage. When I run the project, it always gives me the following error for the bold red line.

TypeError: Error #2007: Parameter child must be non-null.

          at flash.display::DisplayObjectContainer/addChildAt()

          at fl.controls::BaseButton/drawBackground()

          at fl.controls::LabelButton/draw()

          at fl.controls::Button/draw()

          at fl.core::UIComponent/callLaterDispatcher()

Pleae help me out to get rid of this problem. Thanks in advance.

Thanks,

momersaleem