Al realizar doble clic sobre un listview en blanco lanza error

[wolfran_hack]

Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, Menus, ImgList, ExtCtrls, StdCtrls, OleCtrls, SHDocVw, ComCtrls, Buttons;

type
  TForm1 = class(TForm)
    GroupBox2: TGroupBox;
    BitBtn1: TBitBtn;
    ListView1: TListView;
    Edit1: TEdit;
    procedure BitBtn1Click(Sender: TObject);
    procedure OnDbleCkic(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  DirIP: String;
  Queue: String;

implementation

uses Unit2;

{$R *.dfm}

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
Form2.Show;
end;

procedure TForm1.OnDbleCkic(Sender: TObject);
begin
/// lo que queremos que haga al hacer doble click.
Edit1.Text := ListView1.Selected.Caption;
end;

end.