Since my schema was autogenerated with notnull:false, I think it should be set this way. So the Validator, when called, has to use this parameter do do de validation.

I got mine working with:

/**

 * Doctrine_Validator_Notnull

 *

 * @package     Doctrine

 * @subpackage  Validator

 * @license     http://www.opensource.org/licenses/lgpl-license.php LGPL

 * @link        www.phpdoctrine.com

 * @since       1.0

 * @version     $Revision: 2702 $

 * @author      Konsta Vesterinen <kvesteri@cc.hut.fi>

 */

class Doctrine_Validator_Notnull extends Doctrine_Validator_Driver

{

    /**

     * checks that given value isn't null

     *

     * @param mixed $value

     * @return boolean

     */

    public function validate($value)

    {

            if ( $this->getArg('args') === true) { 

          return ($value !== null);

            }

            else {

              return true;

            }

    }

}