I have a model with nullable fields. Upgrading from 3.14 to 3.15 I'm getting this error:
AssertionError: You cannot call .save() on a serializer with invalid data.

When I print theserializer.errors afterserializer.is_valid(), it says those fields are required. Is it possible that this is a bug, or do I have to manually override the field in the serializer to have therequired=False kwarg?