As you have probably seen, when you use array filter, the auto-generated relevance for each sub-question is something like this:
You want the auto-generated code to be:
(!is_empty(q1_sq3.NAOK) and q1_sq3.NAOK != 0)
There are two ways to do that, both of which would require enhancements:
(1) Provide a new advanced question attribute called, perhaps, array_filter_alternate_missing_values, which could be a semi-colon delimited set of values that would be treated by the array_filter as a missing value. The reason for not just using 0 is that authors might want to give users the option to enter values like 888 or 999 to indicate that the choices are not applicable, or that they refuse to answer.
(2) Implement a GUI for sub-question relevance. That way each sub-question could have an additional relevance clause added to it which would be anded to anything auto-generated by the array-filter routines. This approach is more complicated, but would support a common request for that functionality.
/Tom