title: NHibernate Linq - how to create a where statement with IS NOT NULL
body: <p>how can i achieve this query with Nhibernate Linq?</p>
  
  <pre><code>var l = session.CreateQuery("from Auswahl a where a.Returnkey is not null").List&lt;Auswahl&gt;();
  </code></pre>
  
  <p>i tried this but it always returns an empty list.</p>
  
  <pre><code>var l = session.Linq&lt;Auswahl&gt;()
                     .Where(item =&gt; !String.IsNullOrEmpty(item.Returnkey))
                     .Select(item =&gt; item)
                     .ToList();
  </code></pre>