span>     <br />&#160;&#160;&#160; }     <br />} </div>  <p>The line I&#39;ve highlighted seems perfectly reasonable, right? We&#39;re trying to add the &quot;real&quot; non-null value within a value type value, and we know that there <em>is</em> a real value, because we&#39;ve checked it&#39;s not the null value already.</p>  <p>Now think about what the Value property actually does... it checks whether or not it&#39;s the null value, and then returns the real value or throws an exception. But we <em>know</