The CSV file is being generated by a third party using double quotes to define each field value. Any field that is null, or with nothing in the value, is being sent as "". In Loftware, the scripting engine sees the "" as a single double quote ("), not as a null value. As a result, the field requiring print suppression is ignored and the label still prints.
Change the script to search for "\"", rather than "" as the null.