title: SingleOrDefault() method: what is "a default value"?
body: <p>I'm testing for the existence of a user record in the following statement:</p>
  
  <pre><code>if (fromUser.AllFriends.Where(af =&gt; af.FriendUserID == toUserID).SingleOrDefault() == ???
  </code></pre>
  
  <p>Given the documentation:</p>
  
  <p><em>Returns a single, specific element of a sequence, <strong>or a default value</strong> if that element is not found.</em></p>
  
  <p>What does the bold text refer to?  What the heck am I testing for in my if statement?</p>
  
  <p>A serious question that probably sounds simple and ridiculous to most.</p>
  
  <p>Thanks.</p>