title: Cannot implicitly convert 'System.TimeSpan?' to 'System.TimeSpan'
body: <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>