试图向Telerik RadGrid添加空白行时出现空引用异常

有人能告诉我为什么我一直得到一个NULL引用异常时，试图执行下面的添加?这只发生在ObservableCollection开始为空的时候。如果集合中从一开始就有数据，则可以正常工作。

加载ObservableCollection，设置采集ViewSource:

private void LoadCodeSets()
{
    this.codeSetData = new ObservableCollection<CodeSet>();
    var query = from c in context.CodeSets
                where c.LogicallyDeleted == 0
                orderby c.CodeSetID ascending
                select c;
    foreach (CodeSet c in query)
    {
        this.codeSetData.Add(c);
        this.codeSetView = (ListCollectionView)CollectionViewSource.GetDefaultView(codeSetData);
        this.codeSetRadGridView.ItemsSource = this.codeSetView;
    }
}

将新记录添加到空数据网格

private void Add_CodeSet_Click(object sender, RoutedEventArgs e)
{
    try
    {
        bool doesCodeSetExist = false;
        if (codeSetView == null)
        {
            codeSetView.AddNewItem(new CodeSet());
        }
        else
        {
            foreach (CodeSet cs in codeSetView)
            {
                if (cs.CodeSetID == 0)
                {
                    doesCodeSetExist = true;
                    this.lblMessages.Foreground = Brushes.Red;
                    this.lblMessages.FontWeight = System.Windows.FontWeights.ExtraBold;
                    this.lblMessages.Content = "Please fill in new user form and click Save User.";
                    this.lblMessages.Visibility = Visibility.Visible;
                }
            }
            if (!doesCodeSetExist)
            {
                CodeSet newCodeSet = new CodeSet();
                codeSetView.AddNewItem(newCodeSet);
            }
        }
    }
    catch (Exception ex)
    {
        Error.LogError(ex);
    }
}

if (codeSetView == null)
{
    codeSetView.AddNewItem(new CodeSet());
}

if (codeSetView == null)
{
    codeSetView = new ...... or (ListCollectionView)CollectionViewSource.GetDefaultView(codeSetData);
    codeSetView.AddNewItem(new CodeSet());
}