The attached program should have worked. At the very least there is a usability concern about how to correctly use NeverSerializeDefaultValueConvention, but I think there are also one or more minor bugs lurking (in particular, setting the default value forces SerializeDefaultValue to true overriding the value provided by the convention).

See also: https://groups.google.com/group/mongodb-user/browse_thread/thread/8ee0a96225e22c4b#