This issue was reported as part of this dspace-tech email thread:
The cause seems to be that the AbstractMETSIngester improperly requires that every <fileGrp> element (which represents a DSpace Bundle) has a "ADMID" attribute:
The METS Schema does NOT require the <fileGrp> element to have an ADMID. In fact, our AbstractMETSDisseminator class doesn't even add an ADMID to the <fileGrp> if a Bundle doesn't have any administrative metadata associated with it:
This bug should only affect users who are exporting packages using the "METS" format. When exporting using the "AIP" format, every <fileGrp> (representing a Bundle) is given an ADMID attribute which references the Bundle's access policy metadata (The "METS" format does not contain this access policy information).
Although untested/unverified, I believe the proper fix would be to:
(1) Ensure a missing ADMID does not throw an error in the AbstractMETSIngester, i.e. remove this logic: https://github.com/DSpace/DSpace/blob/master/dspace-api/src/main/java/org/dspace/content/packager/AbstractMETSIngester.java#L848
(2) However, if the ADMID does not exist, then skip over any "crosswalking" of Bundle-related metadata (As the ADMID is what references metadata that needs crosswalking). I.e. this line needs to check if an ADMID exists: