Markup extension that returns the values of an enum type

EnumValuesExtension.cs

public class EnumValuesExtension : MarkupExtension
{
    public EnumValuesExtension()
    {
    }
    
    public EnumValuesExtension(Type enumType)
    {
        EnumType = null;
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        if (EnumType == null)
            throw new InvalidOperationException("EnumType was not specified");

        object[] values = Enum.GetValues(EnumType).Cast<object>().ToArray();
        if (InsertNull == NullPosition.Before)
            values = new object[] { null }.Concat(values).ToArray();
        else if (InsertNull == NullPosition.After)
            values = values.Concat(new object[] { null }).ToArray();
        return values;
    }
    
    [ConstructorArgument("enumType")]
    public Type EnumType { get; set; }
    public NullPosition InsertNull { get; set; }
}

public enum NullPosition
{
    None,
    Before,
    After
}

Sample.xaml

<ComboBox ItemsSource="{my:EnumValues my:MyEnum, InsertNull=Before}">
    ...
</ComboBox>