No way to specify 'is empty' in searchRecords criteria

No way to specify 'is empty' in searchRecords criteria

I need a custom function that iterates through a set of records that have an empty field, like this:

module_records = zoho.crm.searchRecords("Leads", "(Territory Code|is empty|*)",1,200);

Unfortunately the criteria doesn't work.

How am I supposed to write the criteria that the field "Territory Code" IS EMPTY ?

I'm also interested in to know how I can combine criteria in the above script.
E.g.
Territory Code is empty AND Country is not empty

Thanks