Cannot nullify model fields using API
It is not possible to set a model's field to
nil using the API. This affects all the endpoints where
API::Helpers#attributes_for_keys is used.
Steps to reproduce
See a failing test case !5696 (closed)
This is easy to fix from the point of view of the changes needed, but it may break some clients of the API. Clearly this is a bug, but people may rely on this bug in their code.