title: Why is this extension method not working?
body: <p>I can't get to do what I want. I only want accounts for non-international representatives. But when I call ActiveAccounts(), I'm not getting null, I'm getting an enumerable, which then includes null. What am I doing wrong here? Help please.</p>
  
  <pre><code>public static class AccountExt
  {
      public static IEnumerable&lt;Account&gt; ActiveAccounts( this AccountRep rep )
      {
          if( rep == null )
              throw new ArgumentNullException();
          if( rep.IsInternational )
              yield return null;
  
          foreach( var acc in rep.FetchAccounts() )
          {
              if( acc.IsActive )
                  yield return acc;
          }
      }
  }
  </code></pre>