CFPDF Action="Merge" requiring "pages" attribute

[mykaf73934846]

I'm merging some PDFs with

<cfpdf action="merge" source="#arrayToList(arguments.PDFsToMerge)#" destination="#finalPDFDocument#" overwrite="yes" >

But I'm getting the error "The pages attribute is not specified for the MERGE action in the cfpdf tag." 

I have used this tag/action before without requiring the "pages" attribute, since, per the documentation, it's optional for the "merge" action. Why is it requiring this?