C# – Solution to binding errors thrown by setting Image.Source to a binding to null. (suppression?)

I've got a scenario where I have Image Sources set to null which are resolved later and then displayed. Any good way to prevent my code from throwing binding errors?

An example:

System.Windows.Data Error: 23 : Cannot convert '' from type '' to type 'System.Windows.Media.ImageSource' for 'en-US' culture with default conversions; consider using Converter property of Binding. NotSupportedException:'System.NotSupportedException: ImageSourceConverter cannot convert from (null).
at System.ComponentModel.TypeConverter.GetConvertFromException(Object value)
at System.Windows.Media.ImageSourceConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
at MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, DependencyObject targetElement, CultureInfo culture, Boolean isForward)'

XAML

<Image x:Name="image" Height="Auto" Width="Auto" Opacity="0">
    <Image.Effect>
        <DropShadowEffect/>
    </Image.Effect>
    <Image.Source>
        <Binding Path="ImageStream">
            <Binding.ValidationRules>
                <validationRules:NotNullStreamValidationRule/>
            </Binding.ValidationRules>
        </Binding>
    </Image.Source>
</Image>

C#

namespace FlickrDemo.ViewModel
{
    public class FlickrPhotoViewModel : ViewModelBase
    {
        public const string ImageStreamPropertyName = "ImageStream";

        private Stream _imageStream = null;

        public Stream ImageStream
        {
            get
            {
                return _imageStream;
            }

            set
            {
                if (_imageStream == value)
                {
                    return;
                }
                _imageStream = value;

                RaisePropertyChanged(ImageStreamPropertyName);
            }
        }

        public const string IsLoadingPropertyName = "IsLoading";

        private bool _isLoading = false;

        public bool IsLoading
        {
            get
            {
                return _isLoading;
            }

            set
            {
                if (_isLoading == value)
                {
                    return;
                }

                _isLoading = value;

                RaisePropertyChanged(IsLoadingPropertyName);
            }
        }

        public const string PhotoIDPropertyName = "PhotoID";

        private string _photoID = String.Empty;

        public string PhotoID
        {
            get
            {
                return _photoID;
            }

            set
            {
                if (_photoID == value)
                {
                    return;
                }

                var oldValue = _photoID;
                _photoID = value;

                RaisePropertyChanged(PhotoIDPropertyName);
            }
        }

        public FlickrPhotoViewModel(string photoID)
        {
            this.PropertyChanged += async (s, e) =>
            {
                if (e.PropertyName == ImageStreamPropertyName)
                {
                    if (!(ImageStream == null || ImageStream == Stream.Null))
                    {
                        IsLoading = false;
                    }
                }
            };
            IsLoading = true;
            PhotoID = photoID;
        }
    }
}