public void Execute(object parameter)
            {
                var target = _reference.Target as IViewModel;

                if (target == null)
                {
                    return;
                }
                if (NestedCommand == null)
                {
                    _provider.TryCloseViewModel(target, parameter);
                }
                else
                {
                    NestedCommand.Execute(parameter);
                }
            }