Null exception in ZXing.Mobile.ZXingScannnerControl.OnTap

I sometime got this Null exception in my app. I fixed this issue by adding a check of _reader variable:
        protected override void OnTap(System.Windows.Input.GestureEventArgs e)
        {
            base.OnTap(e);
            if (_reader != null)
            {
                _reader.Focus();
            }
        }
Thanks for greate project!
