Controller/CustomFieldsGroupController.php
private function createMakeDefaultForm(CustomFieldsGroup $group = null)
    {
        return $this->createFormBuilder($group, array(
                    'method' => 'POST',
                    'action' => $this->generateUrl('customfieldsgroup_makedefault')
                ))
                ->add('id', 'hidden')
                ->add('submit', 'submit', array('label' => 'Make default'))
                ->getForm();
    }
private function createMakeDefaultForm(CustomFieldsGroup $group = null)
    {
        return $this->createFormBuilder($group, array(
                    'method' => 'POST',
                    'action' => $this->generateUrl('customfieldsgroup_makedefault')
                ))
                ->add('id', 'hidden')
                ->add('submit', 'submit', array('label' => 'Make default'))
                ->getForm();
    }
create a form to make the group default

@param CustomFieldsGroup $group
@return \Symfony\Component\Form\Form