It would be good to be able to expire / empty an evar explicitly / manually.
Therefore it would be best to have a keyword (like eg. "Null") which can be set as a value for the evar, that leads to an instant clear of the value / expiration of that evar.
So if I have an evarX which contains a value I would like to be able submit evarX="null".
From that call onward this evar should behave as if it has never been set.