title: Linq2SQL: Always get .Sum() to return 0 instead of null
body: <p>Is there any way (through a extention mechanism?) to get the <code>Sum()</code> function to allways return 0.</p>
  
  <p>My workaround now is to write like this, but I'm hoping there's a better solution?</p>
  
  <pre><code>((int?)e.CampaignCodes.Sum(f =&gt; f.Enquiries.Count()) ?? 0),
  </code></pre>