ravendb/ravendb — pull request #487 by jstrassburg (2012-07-17 19:13:35+00:00)
Title: Per this discussion on the google group: https://groups.google.com/d/topic/ravendb/FrwYvsV_Kc0/discussion

Overriding these methods of JsonWriter to throw NotSupportedException.
If a client implemented a custom JsonConverter using either their object
would fail to save from a later NullReferenceException. This makes it
clear that these methods are not supported.