title: attempt to create saveOrUpdate event with null entity
body: <p>I have a GWT app that makes an RPC call to a server to save/create a new entity. However, the Spring-Hibernate back-end throws an exception with the following error message:</p>
  
  <pre><code>attempt to create saveOrUpdate event with null entity
  </code></pre>
  
  <p>I'm not sure what that means. What's null? If it's a new entity I am saving, I am expecting to have the <code>id</code> field be <code>null</code> or possibly <code>0</code>, and then have hibernate fill it. Is this expectation correct?</p>