During deserialization, we do not call custom deserializer if the field is to be set to null. Moreover, changed the logic to set fields to null only if explicitly indicated in the incoming Json. This is different from past behavior where all fields not mentioned in incoming Json were set to null. Now they are set to whatever the default constructor will do.
This is done since it is improper to throw a parse exception from serializers. Moreover, the serializers dont deal with external input, they deal with classes, so they need not guard against spurious input.
This helps is handling cases where the user is using their own subclass of Collection or Map.
Updated ParameterizedTypeHandlerMap to return the handler corresponding to Map and Collection for subclasses if user has not specified a specific handler.
Fixed the logic in JsonTreeNavigator to not output a comma if the first field of an object was null.
