Getting Error while Using Router Delegate

While doing setup related to Router Delegate getting below error

Error:

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following StateError was thrown building IconTheme(color: Color(0xdd000000)):
Bad state: No element

My code :

@override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      debugShowCheckedModeBanner: false,
      title: 'Something',
      theme: _themeStore.selectedThemeData,
      routeInformationParser: parser, routerDelegate: delegate,
      localizationsDelegates: context.localizationDelegates,
      supportedLocales: context.supportedLocales,
      locale: context.locale,
    );
  }