How to use form event listener in Sonata Admin

SubjectInsideFunctionAdmin.php

<?php

use Sonata\AdminBundle\Admin\Admin;
use Sonata\AdminBundle\Form\FormMapper;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;

class SubjectOutsideFunctionAdmin extends Admin
{
    protected function configureFormFields(FormMapper $formMapper)
    {
        $admin = $this;

        $formMapper->getFormBuilder()->addEventListener(FormEvents::PRE_SET_DATA,
            function (FormEvent $event) use ($formMapper, $admin) {

            $form = $event->getForm();
            $subject = $admin->getSubject($event->getData());

            if ($form->has('durationType')) {
                $form->remove('durationType');
            }

            $disabled = $subject->getAbsenceType() === null ? true : false;

            $durationType =  $formMapper->getFormBuilder()->getFormFactory()->createNamed('durationType', 'sonata_type_translatable_choice', null, array(
                        'choices' => DurationType::getTypeList(),
                        'catalogue' => 'TimekeepingBundle',
                        'expanded' => true,
                        'required' => false,
                        'empty_value' => 'type_not_specified',
                        'attr' => array('disabled' => $disabled),
                        'disabled' => $disabled,
                        'auto_initialize' => false // Automatic initialization is only supported on root forms.
                    ));

            $form->add($durationType);
        });
    }
}

SubjectOutsideFunctionAdmin.php

<?php

use Sonata\AdminBundle\Admin\Admin;
use Sonata\AdminBundle\Form\FormMapper;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;

class SubjectOutsideFunctionAdmin extends Admin
{
    protected function configureFormFields(FormMapper $formMapper)
    {
            $subject = $this->getSubject();

            if ($subject->getId() !== null) {
                $formMapper->getFormBuilder()->addEventListener(FormEvents::PRE_SET_DATA,
                    function (FormEvent $event) use ($formMapper, $subject) {

                    $form = $event->getForm();

                    if ($form->has('durationType')) {
                        $form->remove('durationType');
                    }

                    $disabled = $subject->getAbsenceType() === null ? true : false;

                    $durationType =  $formMapper->getFormBuilder()->getFormFactory()->createNamed('durationType', 'sonata_type_translatable_choice', null, array(
                                'choices' => DurationType::getTypeList(),
                                'catalogue' => 'TimekeepingBundle',
                                'expanded' => true,
                                'required' => false,
                                'empty_value' => 'type_not_specified',
                                'attr' => array('disabled' => $disabled),
                                'disabled' => $disabled,
                                'auto_initialize' => false // Automatic initialization is only supported on root forms.
                            ));

                    $form->add($durationType);
                });
            }
        }
    }
}

Issues related to data setting:

• sonata-project/SonataAdminBundle#2076
• sonata-project/SonataAdminBundle#3080

i have this error : Please provide a valid sonata_field_description option
related issue : sonata-project/SonataAdminBundle#3072