title: "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json
body: <p>I have 2 POCO classes -- Contact and TrainingSeminar -- that joined in a many-to-many relationship using EF5</p>
  
  <p>In the Contacts odata controller, I want to be able to return the TrainingSeminars that a contact is registered for...so I have the following controller method</p>
  
  <pre><code>public IQueryable&lt;TrainingSeminar&gt; GetTrainingSeminars([FromODataUri] int key)
  {
      var contact = _context.Contacts.Find(key);
      var seminars = contact.TrainingSeminars.ToList();
      return seminars as IQueryable&lt;TrainingSeminar&gt;;
  }
  </code></pre>
  
  <p>When I debug in Visual Studio, the return object "seminars" has 2 items but I get the following error in Fiddler: </p>
  
  <blockquote>
    <p>"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json...."message":"Cannot serialize a null 'feed'</p>
  </blockquote>