Andriod native plugin: AndroidAdMob.Client.CreateAdBanner not working

I am using the new android Native plugin 7.6, for some reason , whenever i call the AndroidAdMob.Client.CreateAdBanner method , i get a null reference pointing towards the AndroidAddMobController scripts CreateAdBanner method at this line "_banners.Add(bannner.id, bannner);"; I get this error with the example scene , the "GoogleAdPrefabSolution" scene aswell.

     public GoogleMobileAdBanner CreateAdBanner(int x, int y, BannerSize size)   {
     if(!_IsInited) {
     Debug.LogWarning ("CreateBannerAd shoudl be called only after Init function. Call ignored");
         return null;
     }
 AndroidADBanner bannner = new AndroidADBanner(x, y, size, GADBannerIdFactory.nextId);
     Debug.Log (bannner.id);
     **_banners.Add(bannner.id, bannner);**
     return bannner;
     
 }

"NullReferenceException: Object reference not set to an instance of an object AndroidAdMobController.CreateAdBanner (Int32 x, Int32 y, GADBannerSize size) (at Assets/Extensions/GooglePlayCommon/Ad/AndroidAdMobController.cs:223)"

What am i missing here , as i recall , i did follow all the steps.

here's the code i wrote

  private const string MY_BANNERS_AD_UNIT_ID = "xxxxxxx";


  void Start () {

     AndroidAdMobController.Instance.Init (MY_BANNERS_AD_UNIT_ID);
           CreateBannerCustomPos ();
          ShowBanner ();
      }

  public  void CreateBannerCustomPos() {
            banner1 = AndroidAdMob.Client.CreateAdBanner(300, 100, GADBannerSize.BANNER);
  }

    private void ShowBanner() {
     Debug.Log ("ShowBanner");
     banner1.Show ();
 }

   P.s Even tried using  AndroidAdMobController.Instance.CreateAdBanner(), but get the same error