Campo extraData no requerido

EventListener/SonataAdminConfigureListener.php

@@ -31,6 +31,7 @@ class SonataAdminConfigureListener
         if ($event->getMapper()->has('extraData')) {
             $formMapper = $event->getMapper();
             $formMapper->add('extraData', TextareaType::class, array(
+                'required' => false,
                 'help' => $this->translator->trans('help.json_format', array(), 'ExtraDataBundle'),
             ));
         }