public void SetDiscriminatorValue()
        {
            var subClass = typeof(Inherited);
            var mapdoc = new HbmMapping();
            var mapper = new SubclassMapper(subClass, mapdoc);
            mapper.DiscriminatorValue("blah");

            var hbmEntity = mapdoc.SubClasses[0];

            hbmEntity.DiscriminatorValue.Should().Be("blah");

            mapper.DiscriminatorValue(null);
            hbmEntity.DiscriminatorValue.Should().Be("null");
        }