Исключение при Drag and Drop TextBox - са

хотел создать свой редактор блок-схем, но столкнулся с проблемой. Реализовал Drag and Drop для блока у которого есть TextBox и при переносе блока зажав курсор на TextBox происходит исключение. Если сделать TextBlock, а не TextBox то исключения нет, но нельзя редактировать текст.

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    public class Block
    {
        private Canvas? canvas;
        private TextBox? textBox;

        public UIElement GetUIElementWithoutCreat() =>
            canvas;
        public UIElement GetUIElement()
        {
            if (canvas == null)
            {
                canvas = new Canvas();
                textBox = new TextBox();
                canvas.Width = 140;
                canvas.Height = 60;
                textBox.Width = 140;
                textBox.Height = 20;
                textBox.Text = "Действие";
                canvas.Background = Brushes.Green;
                Canvas.SetTop(textBox, 20);
                canvas.Children.Add(textBox);
            }
            canvas.MouseMove += MouseMoveBlockForMovements;
            return canvas;
        }
        private void MouseMoveBlockForMovements(object sender, MouseEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                BlockForMovements instanceOfBlockForMovements = new BlockForMovements(sender);
                var dataObjectInformation = new DataObject(typeof(BlockForMovements), instanceOfBlockForMovements);
                DragDrop.DoDragDrop(sender as DependencyObject, dataObjectInformation, DragDropEffects.Copy);
            }
            e.Handled = true;
        }
    }

    public class BlockForMovements
    {
        public object sender { get; private set; }
        public BlockForMovements(object sender) =>
            this.sender = sender;
    }

    private void block_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.LeftButton == MouseButtonState.Pressed)
        {
            Block block = new Block();
            DataObject data = new DataObject(typeof(Block), block);
            DragDrop.DoDragDrop(sender as DependencyObject, data, DragDropEffects.Copy);
        }
    }

    private void destination_Drop(object sender, DragEventArgs e)
    {
        if (e.Data.GetDataPresent(typeof(Block)))
        {
            Point point = e.GetPosition(destination);
            Block block = new Block();
            Canvas.SetLeft(block.GetUIElement(), point.X);
            Canvas.SetTop(block.GetUIElement(), point.Y);
        }
        e.Handled = true;
    }

    private void destination_DragOver(object sender, DragEventArgs e)
    {
        if (e.Data.GetDataPresent(typeof(Block)))
        {
            e.Effects = DragDropEffects.Copy;
            Point point = e.GetPosition(destination);
            Block block = (Block)e.Data.GetData(typeof(Block));
            UIElement uIElement;
            if (block.GetUIElementWithoutCreat() == null)
            {
                uIElement = ((Block)e.Data.GetData(typeof(Block))).GetUIElement();
                destination.Children.Add(uIElement);
            }
            else
                uIElement = ((Block)e.Data.GetData(typeof(Block))).GetUIElement();

            Canvas.SetLeft(uIElement, point.X + 1);
            Canvas.SetTop(uIElement, point.Y + 1);
        }
        else if (e.Data.GetDataPresent(typeof(BlockForMovements)))
        {
            e.Effects = DragDropEffects.Copy;
            Point position = e.GetPosition(destination);
            BlockForMovements resultTransferInformation = (BlockForMovements)e.Data.GetData(typeof(BlockForMovements));
            object transferInformation = resultTransferInformation.sender;
            Canvas.SetLeft((UIElement)transferInformation, position.X + 1);
            Canvas.SetTop((UIElement)transferInformation, position.Y + 1);

        }
        else
            e.Effects = DragDropEffects.None;
    }
}'

<Window x:Class="WpfApp2.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:WpfApp2"
    mc:Ignorable="d"
    Title="MainWindow" Height="450" Width="800">
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="150"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <Canvas Grid.Column="1" 
            Name="destination"
            Background="Gray" 
            AllowDrop="True" 
            DragOver="destination_DragOver" 
            Drop="destination_Drop"/>
    <Grid Grid.Column="0">
        <Grid.RowDefinitions>
            <RowDefinition Height="60"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Canvas Grid.Column="0" Background="Green" Width="140" Height="60" MouseMove="block_MouseMove">
            <TextBox Canvas.Top="20" Text="Действие" TextAlignment="Center" HorizontalAlignment="Center" Width="140"/>
        </Canvas>
    </Grid>
</Grid>

Ссылка на сам проект: https://disk.yandex.ru/d/3veLL5AR2YSycg