[TECH SUPPORT] LPS-50516 Fix

Hey Marcellus,

As you probably have seen, there are tests which are failing because of the way LPS-5016 changed the logic: https://github.com/liferay/liferay-portal/commit/c04dfeaa21c7850502bc7c9ae8b134fd98fe1bc5

With this new commit I'm going back to the original logic to return a Serializable in case of repeatable fields and fix the original issue, too.

Please review the change.

Thanks,
Ákos