Thank you for bringing this to our attention. It seems you have found a bug - I have been able to reproduce this issue locally. Consequently, I have filed a bug ticket here, so that we can track progress on this issue and hopefully include a fix in an upcoming release:
While physical storage reports can only be generated by authenticated users, by default file and item report generation can be launched by anyone, including public users. However, the problem is that the Continue button displays even if there are no file or item-level descriptions available on the target archival unit.
I don't have any solid workarounds to suggest at this time. If you are not using the Reports module, then you could potentially make some local code changes to give the Reports link on the description view page a class or unique ID, and then use CSS to hide it entirely. However, CSS will not work for selectively hiding the Continue button on the reports page only when there are no files or items - this would require further PHP code to check the descendant records, meaning that performance in large hierarchies would also need to be considered.
Hopefully we can address this issue in an upcoming release. In the meantime, apologies for the inconvenience, and thank you again for bringing this issue to our attention!