Implementation
  set renderBoxModel(RenderBoxModel? value) {
  if (value == null) {
    _renderReplaced = null;
    _renderLayoutBox = null;
    _renderWidget = null;
    _renderSVG = null;
  } else if (value is RenderReplaced) {
    _renderReplaced = value;
  } else if (value is RenderLayoutBox) {
    _renderLayoutBox = value;
  } else if (value is RenderWidget) {
    _renderWidget = value;
  } else if (value is RenderSVGShape || value is RenderSVGContainer || value is RenderSVGText) {
    _renderSVG = value;
  } else {
    if (!kReleaseMode) throw FlutterError('Unknown RenderBoxModel value.');
  }
}