4.21.0

Added

• [#7960] Added support for doctrine/collections 2 (@franmomu)

Changed

• [#7962] Made AbstractAdmin::setSubject() use getModelClass() instead of getClass() to check is the subject is allowed (@7ochem)

Fixed

• [#7963] Fix appendFormFieldElement on nested collection named the same as one of the parent fields (@fgueguen)
• [#7961] Fixes ChoiceFieldMaskType behavior inside CollectionType (@Darkabso)
• [#7952] Fix an issue that an exception will be thrown by Pool::getAdminByClass() when the admin code is different from its service id. (@tamcy)
• [#7952] Fix a typo in the deprecation message which is triggered when multiple sonata.admin tags are found in the same service definition. (@tamcy)