update method Null safety

Implementation

void update(
    {bool flash = false,
    BlinkMode blink = BlinkMode.none,
    bool disableWindow = false,
    bool neverReformat = false}) {
  if (ignoreUpdates) {
    return;
  }
  if (_showingX && !neverReformat) {
    currentShowingX = model.formatValue(model.x);
    // In case window enabled setting changed
  }
  final LcdContents c = (blink == BlinkMode.justDigits)
      ? model._newLcdContentsJustDigits()
      : model._newLcdContents(disableWindow: disableWindow);
  if (blink.blinking || model.errorBlink) {
    bool on = true;
    final blank = LcdContents.blank();
    final Duration d;
    if (blink.blinking) {
      d = const Duration(milliseconds: 400);
    } else {
      d = const Duration(milliseconds: 200);
    }

    final t = Timer.periodic(d, (_) {
      on = !on;
      show(on ? c : blank);
    });
    c._myTimer = t;
    blank._myTimer = t;
    show(c);
  } else if (flash) {
    final t = Timer(const Duration(milliseconds: 40), () {
      show(c);
    });
    c._myTimer = t;
    show(LcdContents.blank().._myTimer = t);
  } else {
    c._myTimer = null;
    show(c);
  }
}