Empty dates in querystring-search return string of None

[JeffersonBledsoe]

The content API correctly returns null for an item, whilst the querystring-search returns "None". For example, "effective": null is returned as "EffectiveDate": "None"

Example API response from Plone6 demo site (6.0.0rc1)

https://6.demo.plone.org/++api++/@querystring-search:

{
    "@id": "https://6.demo.plone.org/@querystring-search",
    "items": [
        {
            "@id": "https://6.demo.plone.org",
            "@type": "Plone Site",
            "CreationDate": "2022-12-07T00:00:25+00:00",
            "Creator": "admin",
            "Date": "2022-12-07T18:44:34+00:00",
            "Description": "This site is a demonstration of Plone 6 with Volto for its frontend.",
            "EffectiveDate": "None",
            "ExpirationDate": "None",
            "ModificationDate": "2022-12-07T18:44:34+00:00",
            ...
        },
        ...
    ],
    ...
}