[net.sf.hibernate.AssertionFailure] an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
net.sf.hibernate.AssertionFailure: null id in entry (don't flush the Session after an exception occurs)
        at net.sf.hibernate.impl.SessionImpl.checkId(SessionImpl.java:2630)
        at net.sf.hibernate.impl.SessionImpl.flushEntity(SessionImpl.java:2454)
        at net.sf.hibernate.impl.SessionImpl.flushEntities(SessionImpl.java:2447)
        at net.sf.hibernate.impl.SessionImpl.flushEverything(SessionImpl.java:2249)
        at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2228)
        at za.co.quirk.milk.action.dairy.DairyImportAction.execute(DairyImportAction.java:101)
        at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
        at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
        at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
        at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:763)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
....

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

    <class name="za.co.quirk.milk.model.Contact" table="contact">
        <id name="id">
           <generator class="native"/>
        </id>
        ....

    </class>
   
</hibernate-mapping>

    for( int row = 2; ( line = parser.getNextLine() ) != null; row++ )
    { 
.....

      Contact contact = (Contact)addressMap.get( email );
      if( contact == null )
      {
        contact = new Contact();
      }
     
.....

      session.saveOrUpdate( contact );
      if( row % 256 == 0 )
      {
        session.flush();
      }
    }