I'm receiving an error ('The object does not contain any PDF documents to be send for signing.') when trying to use the docusign integration feature 'send with DocuSign' on a document collection (that obviously includes PDF files). Is this simply unsupported or should this normally work? In the documentation ('DocuSign Integreation.pdf') only multifiles are mentioned, and those work as expected. While it is not that hard to work around, similiar behaviour for a document collection would be nice in this instance.