How to use the tns-core-modules/utils/types.isNullOrUndefined function in tns-core-modules

refresh() {
    Log.D(`refresh()`);
    if (!this.nativeView) {
      return;
    }

    let itemsCount = this.getItemCount();
    Log.D(`Items count: `, itemsCount);
    if(isNullOrUndefined(itemsCount)){
      return;
    }

    // Using 'items' property and 'itemTemplate' to populate Carousel. Remove all parent children first then add all items.
    if (!isNullOrUndefined(this.itemTemplate)) {
      Log.D(`Using template mode`);
      this.removeChildren();
      for (let i = 0; i < itemsCount; i++) {
        const viewToAdd = !isNullOrUndefined(this.itemTemplate) ? parse(this.itemTemplate, this) : this._getDefaultItemContent(i);
        const dataItem = this._getDataItem(i);
        viewToAdd.bindingContext = dataItem;
        this.addChild(viewToAdd);
      }
    }
    
    // Notify adapter and indicatorView that items have changed. 

var _this = this;
        this.logMsg("activity: " + this.Config.activity, SocialLogin_common_1.LOGTAG_INIT_ENV);
        if (types_1.isNullOrUndefined(this.Config.activity)) {
            this.Config.activity = application_1.android.foregroundActivity || application_1.android.startActivity;
        }
        // Google
        if (this.Config.google.initialize) {
            result = this.initGoogle(result);
        }
        // Facebook
        if (this.Config.facebook.initialize) {
            result = this.initFacebook(result);
        }
        // Twitter
        if (!types_1.isNullOrUndefined(this.Config.twitter.key) &&
            !types_1.isNullOrUndefined(this.Config.twitter.secret)) {
            result = this.initTwitter(result);
        }
        if (!types_1.isNullOrUndefined(this.Config.activity)) {
            var onLoginResult_1 = function (_a) {
                var requestCode = _a.requestCode, resultCode = _a.resultCode, intent = _a.intent;
                if (requestCode === _this._rcGoogleSignIn || requestCode === _this._rcFacebookSignIn) {
                    var resultCtx = {};
                    var callback = _this._loginCallback;
                    var activityResultHandled = false;
                    try {
                        if (requestCode === _this._rcGoogleSignIn) {
                            resultCtx.provider = "google";
                            activityResultHandled = true;
                            if (resultCode === android.app.Activity.RESULT_OK) {
                                _this.logMsg("OK", LOGTAG_ON_ACTIVITY_RESULT);
                                var signInResult = com.google.android.gms.auth.api.Auth.GoogleSignInApi.getSignInResultFromIntent(intent);

refresh() {
    Log.D(`refresh()`);
    if (!this.isLoaded || !this.nativeView) {
      this._isDirty = true;
      return;
    }

    this._isDirty = false;
    this.nativeView.setItems(NSMutableArray.new());


    if (isNullOrUndefined(this.itemTemplate)) {
      Log.D(`Using generic-mode`);
      const nsArray = NSMutableArray.new();
      Log.D(`children count: `, this.getChildrenCount());
      this.eachChildView(staticView => {
        if (staticView instanceof CarouselItem) {
          staticView.width = this.width;
          staticView.height = this.height;
          const dkCarouselViewItem1 = new DKCarouselViewItem();
          dkCarouselViewItem1.view = staticView.ios;
          nsArray.addObject(dkCarouselViewItem1);
        }
        return true;
      });
      this.nativeView.setItems(nsArray);
      Log.D(`items set: `, nsArray.count);
    }

addDatabaseChangeListener(callback: any) {
        const token = this.ios.addChangeListener((change: any) => {
            if (callback && typeof callback === 'function') {
                const ids = [];
                const documentIds = change.documentIDs;
                const size = documentIds.count;
                for (let i = 0; i < size; i++) {
                    const item = documentIds[i];
                    ids.push(item);
                }
                callback(ids);
            }
        });
        if (!types.isNullOrUndefined(token)) {
            this._listenerMap[callback] = token;
        }
    }

getItemCount() {
      let result;
      if (isNullOrUndefined(this.owner.get().items) || !isNumber(this.owner.get().items.length)) {
        result = this.owner ? this.owner.get()._childrenCount : 0;
      } else {
        result = this.owner ? this.owner.get().items.length : 0;
      }
      CLog(CLogTypes.info, `CardStackAdapter getCount result = ${result}`);
      return result;
    }
  }

private deserialize(data: any) {
        if (typeof data === 'string' || typeof data === 'number' || typeof data === 'boolean' || typeof data !== 'object') return data;

        if (types.isNullOrUndefined(data)) {
            return data;
        }

        if (data instanceof NSNull) {
            return null;
        }

        if (data instanceof CBLDictionary) {
            const keys = data.keys;
            const length = keys.count;
            const object = {};
            for (let i = 0; i < length; i++) {
                const key = keys.objectAtIndex(i);
                const nativeItem = data.valueForKey(key);
                object[key] = this.deserialize(nativeItem);
            }

removeDatabaseChangeListener(callback: any) {
        const token = this._listenerMap[callback];
        if (!types.isNullOrUndefined(token)) {
            this.android.removeChangeListener(token);
            delete this._listenerMap[callback];
        }
    }

this.eachChildView(staticView => {
        if (staticView instanceof CarouselItem) {
          staticView.width = this.width;
          staticView.height = this.height;
          const dkCarouselViewItem1 = new DKCarouselViewItem();
          dkCarouselViewItem1.view = staticView.ios;
          nsArray.addObject(dkCarouselViewItem1);
        }
        return true;
      });
      this.nativeView.setItems(nsArray);
      Log.D(`items set: `, nsArray.count);
    } 
    else {
      Log.D(`Using template-mode`);
      if(isNullOrUndefined(this.items)){
        Log.D(`Items list is null...`);
        return;
      }

      this.removeChildren();
      const nsArray = NSMutableArray.new();
      const length = this.items.length;
      Log.D(`items length: `, length);

      for (let i = 0; i < length; i++) {
        const viewToAdd = !isNullOrUndefined(this.itemTemplate) ? parse(this.itemTemplate, this) : null;
        if (!viewToAdd) continue;
        const dataItem = this._getDataItem(i);
        viewToAdd.bindingContext = dataItem;
        this.addChild(viewToAdd);
      }