title: Why am I getting "Abstract Error" when working with TStream class?
body: <p>When I try to run the following simple code sequence, I'm getting the <code>Abstract Error</code> error message:</p>
  
  <pre><code>type
    TForm1 = class(TForm)
      Image1: TImage;
      Button1: TButton;
      procedure Button1Click(Sender: TObject);
    private
      { Private declarations }
    public
      { Public declarations }
    end;
  
  procedure TForm1.Button1Click(Sender: TObject);
  var
    ImageStream: TStream;
  begin
    ImageStream := TStream.Create;
    Image1.Picture.Bitmap.SaveToStream(ImageStream);
    ...
  end;
  </code></pre>
  
  <p>I need to extract the stream of an <code>TBitmap</code> for later processing... What am I doing wrong ?</p>