DDX needs a Map or a List?

Hello,

I am trying to understand (on my own without having to ask the experts...) how to generate a PDF package in Livecycle when I have a List (or Map, whatever is needed) to use as input.  From the docs, it appears I can pass in a List of PDF "documents".

I have the following DDX:

<?xml version="1.0" encoding="UTF-8"?>
<DDX xmlns="http://ns.adobe.com/DDX/1.0/" >
<PDF result="pdfPortfolio">
  <PackageFiles>
   <PDF source="pdfList"/>
  </PackageFiles>
</PDF>
</DDX>

I have the "Input Document Map" set to "variable" with "pdfList" selected.

I get an object coersion exception saying it is expecting a Map, but I tried using a map and I can't get that one right either.

Any help would be appreciated!