Javadoc
To request entity references in place of the actual entities, the client issues a GET request with /$ref appended
to the resource path.
If the resource path does not identify an entity or a collection of entities, the service returns 404 Not Found.
If the resource path terminates on a collection, the response MUST be the format-specific representation of a
collection of entity references pointing to the related entities. If no entities are related, the response is the
format-specific representation of an empty collection.
If the resource path terminates on a single entity, the response MUST be the format-specific representation of an
entity reference pointing to the related single entity. If the resource path terminates on a single entity and no
such entity exists, the service returns 404 Not Found.