Good question.

With a PUT, the incoming representation is supposed to replace--wholly--any existing representation. Certainly if the client explicitly nulls out a property, it should be null on the backend. But given PUT semantics I would argue that if the client does not include the property at all, then that amounts to a null or else some default value, but *not* simply ignoring the property.

I would suggest that SDR use HTTP PATCH to accomplish property-level updates.