C# Wpf Custom Converter is created but not called

Question

I've got XAML parse exception "BitmapImage UriSource must be set". While parsing, my converter is created, but Convert() method is not called. What am I doing wrong?

XAML:

<ImageBrush >
    <ImageBrush.ImageSource>
          <BitmapImage UriSource="{Binding Path=Value.Image, Converter={StaticResource imageConverter}, ConverterParameter=Value.Image}" CacheOption="OnLoad"></BitmapImage>
    </ImageBrush.ImageSource>
</ImageBrush>

C#:

public class ImageConverter : IValueConverter
{
    public ImageConverter()
    {
    }
    public object Convert(object value, Type targetType,
                      object parameter, CultureInfo culture)
    {
        try
        {
            return new BitmapImage(new Uri((string)value));
        }
        catch
        {
            return new BitmapImage();
        }
    }

    public object ConvertBack(object value, Type targetType,
                              object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Answer 1

I've found kind of solution. Since I needed to use <BitmapImage> only for setting CacheOption.OnLoad so my local source file would not be locked, I've created custom ImageConverter :

[ValueConversion(typeof(Uri), typeof(BitmapImage))]
public class ImageConverter : IValueConverter
{
    public ImageConverter()
    {
    }
    public object Convert(object value, Type targetType,
                      object parameter, CultureInfo culture)
    {
        try
        {
            if(value == null)
            {
                return null;
            }
            var image = new BitmapImage();
            image.BeginInit();
            image.UriSource = value is Uri ? (Uri)value : new Uri(value.ToString());
            image.CacheOption = BitmapCacheOption.OnLoad;
            image.EndInit();
            return image;               
        }
        catch
        {
            return null;
        }
    }

    public object ConvertBack(object value, Type targetType,
                              object parameter, CultureInfo culture)
    {
        throw new NotSupportedException("Convert back function is not supported");
    }
}

And XAML:

<ImageBrush ImageSource="{Binding Path=Value.Image, Converter={StaticResource imageConverter}}">
</ImageBrush>