title: C# in my unit test i want to see if it is null or an empty string
body: <p>I'm using Machine spec / Shouldly and testing a mapping profile (mundane work). The mapping expectations are sometimes inconsistent. Sometimes I am seeing an <code>""</code> explicit empty string get returned and sometimes it's a null value. Since we're mapping to a spreadsheet it doesn't matter on that front but it gets a little annoying when asserting.</p>
  
  <p>Is there a way in Machine spec to do something like <code>assertionValue.ShouldEqual(null || "")</code> ?</p>