According to OData-JSON, section 11, an individual property or operation response with value null must be returned as 204 No Content.

I would like to allow an alternative format of 200 OK with empty JSON payload for structured types and

{"@context": "#«primitive type»",
 "value": null}

for primitive types (which was valid in the 4.0 spec).

This is the only way to add instance annotations or control information to the null result.

Use cases:

• Instance annotation containing messages that occurred during the operation (and which may explain why the result is null). One could even argue that in the presence of instance annotations the result is not null and must thus be represented with a payload.
• @deltaLink not only for "sets of results", but also for single-valued results. Could be used to obtain changes to individual properties or related entities, and must then also be issued for a null result.