title: BannerAd variable has not initialized error
body: <p>i get an error that my BannerAd variable is not initialized and my app crash, so i move my _banner in top of code and still not work, i move it inside the state class and still not initialized what should need to do to be initialized ?</p>
  <pre><code>  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    late BannerAd _banner;
    @override
    void didChangeDependencies(){
      super.didChangeDependencies();
  
      final adState = context.read(adStateProvider);
      adState.initialization.then((value)
      {
        setState(() {
          _banner = BannerAd(size: AdSize.banner, adUnitId: adState.bannerAdUniteId, listener: adState.adListener, request: AdRequest())..load();
        });
      });
    }
    @override
    Widget build(BuildContext context) {
  
      return Scaffold(
  
        body: Center(
          child: Column(
  
            mainAxisAlignment: MainAxisAlignment.center,
            children: &lt;Widget&gt;[
              new Text('pub'),
            if(_banner == null)Text('null hhhhhhhhhhhhhhhhhhhhhhhhhhhhh')
        else Expanded(child: AdWidget(ad: _banner),),
  </code></pre>