FileSetCleanUpJob failures (test)

[eporter23]

Describe the bug
Trying to generate a thumbnail in curate-test for a work with a missing thumb results in an error in sidekiq.

FileSetCleanUpJob	
"2322bvq8cv-cor"
NoMethodError: undefined method `uri' for nil:NilClass

To Reproduce
Steps to reproduce the behavior:

1. Go to a work with a complete FileSet that has no thumbnail: https://curate-test.library.emory.edu/concern/file_sets/2322bvq8cv-cor?locale=en
2. Click on Regenerative Derivative
3. Wait to see a confirmation message on the View FileSet page that the job has been submitted
4. Check Sidekiq to see that the job has been sent; wait to see it go through retries and then fail
5. See error "NoMethodError: undefined method `uri' for nil:NilClass"

Expected behavior
A clear and concise description of what you expected to happen.

When trying to generate or regenerate a thumbnail, we should either not see any errors or not see errors related to nil:NilClass

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):
Mac OS Chrome

Additional context
Add any other context about the problem here.

Normally we might see errors related to derivative creation tools or FITS-related errors.

[bwatson78]

This seems to be fixed with the work done for #2492.

[eporter23]

Unfortunately, I'm seeing a recurrence of this today while checking out some FileSets and trying to generate missing thumbs. Example: https://curate-test.library.emory.edu/concern/file_sets/105s7h44t2-cor?locale=en

[eporter23]

Just retried it again, and it went through without failures. I guess I'll close it again.