*:class:`Symfony\\Component\\Serializer\\Normalizer\\DateTimeNormalizer` uses ``datetime_format`` key as date time format;

*:class:`Symfony\\Component\\Serializer\\Normalizer\\AbstractObjectNormalizer` uses ``empty_iterable_as_object`` to preserve empty objects (keeps ``{}`` instead of ``[]`` in JSON);

..versionadded::5.3

..versionadded::5.4

:class:`Symfony\\Component\\Serializer\\Serializer` uses ``empty_arrays_as_object`` to serialize empty array as object (uses ``{}`` instead of ``[]`` in JSON);