Error happened when building Observer, but it was captured since disableErrorBoundaries==true

[rkundnani]

getting this error

Error happened when building Observer, but it was captured since disableErrorBoundaries==true

I/flutter (13988): No observables detected in the build method of Observer I/flutter (13988): Observer constructed from: BondsWebWidgetState.build package:cherry/…/components/webview_bonds_widget.dart:166

code :

widget class :

@override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: _onBackPressed,
      child: Observer(
        builder:(context) { 
          return Scaffold(
          appBar:  viewModel.loadMessageFromNsdl ? AppBar() : null,
          body: Container(
            padding: const EdgeInsets.only(top: kToolbarHeight),
            height: MediaQuery.of(context).size.height,
            child: WebViewWidget(controller: _controller, gestureRecognizers: {
              Factory<DragGestureRecognizer>(
                () => VerticalDragGestureRecognizer(),
              ),
            }),
          ),
        );
         },
      ),
      );
  }

store class:

@observable
  bool loadMessageFromNsdl = false;

  @action
  void toShowAppBarFunction(bool toShowAppBar){
    loadMessageFromNsdl = toShowAppBar;
  }

[amondnet]

@rkundnani

appBar:  viewModel.loadMessageFromNsdl ? AppBar() : null,

Are there any other conditions on this line? Could it be related to the this issue?