Symfony 2.5 - Ajax Autocomplete form type - Querybuilder not supported?

[keebeegee]

Using:

$builder->add(
       'knowledge_area',
       'shtumi_ajax_autocomplete',
       array(
            'label'       => 'Knowledge Area',
            'class'       => 'KeebeegeeCampusBundle:Category',
            'property'    => 'category_name_indent',
            'query_builder' 
                      => function(EntityRepository $er)
                      {
                          $qb = $er->findOneBy(array('static_id' => 3000));
                          return $er->getChildrenQueryBuilder($qb, false, null, 'asc', false );
                      },
            'multiple' => false,
            'empty_value' => 'Choose an option',
            'required' => false                  
        )
);                                          

I get the following exception:

The options "empty_value", "multiple", "query_builder" do not exist. Known options are: "action", "attr", "auto_initialize", ....