json4s/json4s — pull request #72 by efuquen (2013-10-16 14:59:13+00:00)
Title: Better error handling for null AnyVals

Previously if an AnyVal type in a case class was extracted and the value was null in json you would get a vague error in json4s, I believe it was some NullPointer that resulted in a "unknown error" MappingException. By throwing an explicit Mapping Exception with a description of the problem it will be easier to fix problems in json input.