fix serialisation
fix serialisation

OskarStark/SonataMediaBundle,sonata-project/SonataMediaBundle,vyshkant/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,nicolasricci/SonataMediaBundle,hug963/SonataMediaBundle,nicolasricci/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,bgaleotti/SonataMediaBundle,jerome-fix/SonataMediaBundle,nicolasricci/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,OskarStark/SonataMediaBundle,bgaleotti/SonataMediaBundle,hug963/SonataMediaBundle,hug963/SonataMediaBundle,hug963/SonataMediaBundle,jerome-fix/SonataMediaBundle,hug963/SonataMediaBundle,nicolasricci/SonataMediaBundle,OskarStark/SonataMediaBundle,OskarStark/SonataMediaBundle,jerome-fix/SonataMediaBundle,vyshkant/SonataMediaBundle,vyshkant/SonataMediaBundle,jerome-fix/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,vyshkant/SonataMediaBundle,vyshkant/SonataMediaBundle,nicolasricci/SonataMediaBundle,bgaleotti/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,bgaleotti/SonataMediaBundle