why RegisterCallback force my app to stopped

protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
_bundle = savedInstanceState;

        FacebookSdk.SdkInitialize(this.ApplicationContext);
        mCallBackManager = CallbackManagerFactory.Create();

        SetContentView(Resource.Layout.FBLogin);
        button = FindViewById<LoginButton>(Resource.Id.login_button);

        button.SetReadPermissions("user_friends");

        mCallBackManager = CallbackManagerFactory.Create();

         ~~   button.RegisterCallback(mCallBackManager, this);~~

    }

When i place this code button.RegisterCallback(mCallBackManager, this); my app force to close. Can someone assist me with this. Thank you

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