[Zope] Whats the correct way...

Hi! First off all I want to apologize if this question is way off topic here, but I'm stuck and don't know where else to turn my question. Heres the situation: I've made a form to let people search a database where they can choose wich datafields is going to be shown in the result (this is done by several checkboxes). Now if I pass this forms data onto a ZSQLmethod that handles the sql select query (variable names from the checkboxes are handled by '<!--#if names--> - scentences') I end up with an error if not all of the checkboxes are checked out. What would be the correct way to have this handled? (Choose what data to be displayed) Sture Lygren