Binding к вложенным свойствам (ко свойству базового класса), ошибка: "Ключ не может быть неопределенным. Имя параметра: key"

public override DataTemplate SelectTemplate(object item, DependencyObject container)

return base.SelectTemplate(item, container);

//
// Summary:
//     Provides a way to choose a System.Windows.DataTemplate based on the data object
//     and the data-bound element.
public class DataTemplateSelector
{
    //
    // Summary:
    //     When overridden in a derived class, returns a System.Windows.DataTemplate based
    //     on custom logic.
    //
    // Parameters:
    //   item:
    //     The data object for which to select the template.
    //
    //   container:
    //     The data-bound object.
    //
    // Returns:
    //     Returns a System.Windows.DataTemplate or null. The default value is null.
    public virtual DataTemplate SelectTemplate(object item, DependencyObject container)
    {
        return null;
    }
 
    //
    // Summary:
    //     Initializes a new instance of the System.Windows.Controls.DataTemplateSelector
    //     class.
    public DataTemplateSelector()
    {
    }
}

public partial class MainWindow : Window
{
    public MainWindow()
    {
        var vm = new MainViewModel();
 
        DataContext = vm;
 
        InitializeComponent();
    }
}

    public class TableRowObject //: INotifyPropertyChanged
    {
        private VObject _vObject;
        public VObject VObject 
        {
            get => _vObject;
            set { _vObject = value; OnPropertyChanged(); }
        }
 
        public string ToolTip { get; set; }
        public bool IsEnabled { get; set; } = true;
 
        public event PropertyChangedEventHandler PropertyChanged;
 
        protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
            => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using TwoTypeDGrid.Models.Base;
 
namespace TwoTypeDGrid.ViewObjects
{
    //public class TableRowObject //: INotifyPropertyChanged
    //{
    //    private VObject _vObject;
    //    public VObject VObject //{ get; set; }
    //    {
    //        get => _vObject;
    //        set { _vObject = value; OnPropertyChanged(); }
    //    }
 
    //    public string ToolTip { get; set; }
    //    public bool IsEnabled { get; set; } = true;
 
    //    public event PropertyChangedEventHandler PropertyChanged;
 
    //    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    //        => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    //}
 
    public class TableRowObject //: INotifyPropertyChanged
    {
        private VObject _vObject;
        public VObject VObject
        {
            get => _vObject;
            set { _vObject = value; OnPropertyChanged(); }
        }
 
        public string ToolTip { get; set; }
        public bool IsEnabled { get; set; } = true;
 
        public event PropertyChangedEventHandler PropertyChanged;
 
        protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
            => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class VObject // : INotifyPropertyChanged
{
    //public string ExistingCards { get; set; }
    private string _existingCards;
    public string ExistingCards
    {
        get => _existingCards;
        set { _existingCards = value; OnPropertyChanged(); }
    }
 
    public event PropertyChangedEventHandler PropertyChanged;
 
    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
        => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
 
}

new Binding(stringPath);
new Binding(){Path = new PropertyPath(stringPath)};

new Binding()
{
    Path = new PropertyPath("VObject.(0)", typeof(VObject1).GetProperty(nameof(VObject1.ExistingCards)))
};