public void NullInputBreakARule()
        {
            var ruleEnforcer = new NoSelectorMayBeRepeatedInTheRules(
                NoSelectorMayBeRepeatedInTheRules.ConformityOptions.AllowBareSelectorsToBeRepeated
                );

            Assert.Throws <ArgumentNullException>(() => { ruleEnforcer.GetAnyBrokenRules(null).Count(); });
        }