Default value are not properly initialized while using the REST API

This ticket is a split part of NXP-19466.

NXP-19466:

• the default values are not initialized if the doc has not been read.
  > in any Importer
  > in the REST API
  > not in JSF (the doc are read by the engine)
• null props are recognized as phantom
• the default value is set for phantom props (so a null value set on a field with a default value results to the default value)

This issue is about handling the case in the REST API because its isolated in the doc marshaller and can be fixed without refactoring the whole property/doc model.