Unique statement exception for one value

Hi All,

I want to use the unique statement for a model where in a list i have multiple keys and for one key I want that it should be unique across whole list except value 0. Is it possible to add a unique statement with an exception

The leafs listed in the unique statement must be unique across the list, you can not have a unique statement that is unique “except for some value X”.

For that kind of semantics you need a must-statement or an external validation callback.