If you need to be able to represent what looks like a tree of data set - no value - new value do_no_set (sorry about the horrible

If you need to be able to represent what looks like a tree of data set - no value - new value do_no_set (sorry about the horrible tree) then it seems like you should represent the data like that. Pass in action (set/ignore) and value (value for set, no value for ignore). Or even (set/unset/ignore), which allows you to have some sanity checking that, if the action is set, an actual value is provided (and vice versa for unset).