Unexpected red border (validation error) on DataGrid when selecting blank row

Question

When I select (by clicking or by keyboard) blank row on my DataGrid (when I want to add new row), unexpected validation error occurs (but with no exception) - the border of

Answer 1

Here's a general-purpose converter you can use for any DataGrid, binding any kind of item:

    public class DataGridItemConverter : MarkupExtension, IValueConverter
    {
    static DataGridItemConverter converter;

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
        return value;
        }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
        return (value != null && value.GetType() == targetType) ? value : null;
        }

    public override object ProvideValue(IServiceProvider serviceProvider)
        {
        if (converter == null)
            converter = new DataGridItemConverter();
        return converter;
        }
    }

Since it implements MarkupExtension you don't even need to define a static resource, you can just reference it like this:

SelectedItem="{Binding SelectedThing,Converter={conv:DataGridItemConverter}}"