Conditionally require visible fields with sonata_type_choice_field_mask in Sonata Admin

How to conditionally require fields with sonata_type_choice_field_mask :

Ex : if visible : required = true else required = false ?

->add('typeContrat', 'sonata_type_choice_field_mask', array(
                    'choices' => array('CDI' => 'CDI', 'CDD' => 'CDD', 'BDC' => 'BDC'),
                    'map' => array(
                        'CDD' => array('dateFin'),
                        'BDC' => array('dateFin')),
                    'placeholder' => 'Choisir type de contrat',
                    'required' => true,
                    ))
                    ->add('dateFin', 'sonata_type_date_picker', array('format' => 'dd/MM/y', 'label' => 'Date fin'))

I want when 'CDD or BDC' are selected 'dateFin' to become required = true

Thank you!