I am trying to use multiple drop lists as source values for input mapping in a Get List Items rule from a SharePoint List SmartObject.  I'd like the user to be able to select one or more of the five filtering choices (like project, area, status, size, and type).   The drop lists would default to 'All' meaning that there would be no filtering in that category, but the user would select a specific value in any of the drop lists.   This would would be used (or not used, if possible) in the Input Mapping settings.

I have my test set up as a List View and a Header View showing the five columns above inside a Form.  The Header View contains the filter options and a Load Button.  Rules are at the Form level.  I have tried many options and am successful either matching to specific values or to rows with blanks but not able to get it to display rows if only one filter is used and the other filters are left as blank (or 'All').  I have tried using Parameters, data labels, expressions, and Empty Value function.

Can a wildcard be used as a default instead of blank?  If so, what is that wildcard character against a SharePoint List?   I can do this very easily with an InfoPath Form because Query Fields are only set when values are present.  A similar approach in SmartForm would be to load or not load an Input Mapping value only when needed.  Is it possible to do that dynamically?   Thanks for any help!