Cannot implicitly convert 'System.TimeSpan?' to 'System.TimeSpan'
<p>The below code works fine :</p>

<pre><code>DateTime d1 = DateTime.Now;
DateTime d2 = DateTime.Now.AddDays(-1);
int d3 = (int)(d1 - d2).TotalDays;
</code></pre>

<p>But what if I define <code>DateTime</code> as <code>DateTime?</code> :</p>

<pre><code>DateTime? d1 = DateTime.Now;
DateTime? d2 = DateTime.Now.AddDays(-1);
int d3 = (int)(d1 - d2).TotalDays;
</code></pre>

<p>underlined red with error</p>

<blockquote>
  <p>Cannot implicitly convert 'System.TimeSpan?' to 'System.TimeSpan'</p>
</blockquote>

<p>Is it possible to get the difference of number of days between two datetimes that are defined as nullable?</p>