Empty folders are deleted in SIP and METS

[JelleKleevensVAI]

Ideally empty folders should remain.

A content producer may for example use a fixed folder structure per project. Even if some folders remain empty in a project, it still helps the viewer to understand the underlying methodology.

[luis100]

This is tied to the implementation of the EARK SIP specification. The https://github.com/keeps/commons-ip implementation of EARK SIP version 1 does not allow empty folders, and the alpha2 implementation of the EARK SIP version 2 still doesn't support this.

We are checking with the specification authors what is the correct interpretation that will allow the support for empty folders, at least in EARK SIP version 2.