Convert MemoryStream to BitmapImage thrown “System.NullReferenceException”

Question

I am trying to use TagLib to load album art dynamically to Image in WPF. So ,I define a dependency property like this:

   public static readonly DependencyProperty AlbumImageProperty = DependencyProperty.Register(
                "AlbumImage", typeof(BitmapImage), typeof(MainWindow), new PropertyMetadata(default(BitmapImage)));

            public BitmapImage AlbumImage
            {
                get { return (BitmapImage) GetValue(AlbumImageProperty); }
                set { SetValue(AlbumImageProperty, value); }
            }

Then,I write a method to set the image：

private void SetAlbum(string path)
        {
            var file = TagLib.File.Create(path);
            if (file.Tag.Pictures.Length >= 1)
            {
                MemoryStream ms=new MemoryStream(file.Tag.Pictures[0].Data.Data);
                AlbumImage = new BitmapImage();
                AlbumImage.BeginInit();
                AlbumImage.StreamSource = ms;
                AlbumImage.CacheOption = BitmapCacheOption.OnLoad;
                AlbumImage.EndInit();

            }
        }

In the end,I binding it to MainWindow like this:

<Image Name="ImgAlbum" Source="{Binding AlbumImage}" HorizontalAlignment="Left"  UseLayoutRounding="True"/>

But it thrown "System.NullReferenceException" when running to "AlbumImage.EndInit". When I didn't use dependency property to define "AlbumImage" , it can running without throwing Exception , but it also can't update image in MainWindow when the image source is changed.

What should I do to solve it? Thanks.