"git ubuntu queue sync" sometimes crashes

[Robie Basak]

rbasak@diglett:~/review/ubuntu-advantage-tools/git$ git ubuntu queue sync
04/29/2021 19:05:41 - INFO:refs/tags/queue/groovy/unapproved/2ea5a05 is no longer in the queue; deleting
04/29/2021 19:05:44 - INFO:Created annotated tag queue/groovy/unapproved/247c348 for version 27.0~20.10.1
04/29/2021 19:05:48 - INFO:refs/tags/queue/xenial/unapproved/ad547ad is no longer in the queue; deleting
Traceback (most recent call last):
  File "/snap/git-ubuntu/495/usr/bin/git-ubuntu", line 11, in <module>
    load_entry_point('gitubuntu==1.0', 'console_scripts', 'git-ubuntu')()
  File "/snap/git-ubuntu/495/usr/lib/python3/dist-packages/gitubuntu/__main__.py", line 269, in main
    sys.exit(args.func(args))
  File "/snap/git-ubuntu/495/usr/lib/python3/dist-packages/gitubuntu/queue.py", line 111, in cli_main
    return main(
  File "/snap/git-ubuntu/495/usr/lib/python3/dist-packages/gitubuntu/queue.py", line 349, in main
    sync(
  File "/snap/git-ubuntu/495/usr/lib/python3/dist-packages/gitubuntu/queue.py", line 311, in sync
    commit_hash = _commit_upload(repo, upload, series_parent)
  File "/snap/git-ubuntu/495/usr/lib/python3/dist-packages/gitubuntu/queue.py", line 185, in _commit_upload
    for url in _get_upload_source_urls(upload):
  File "/snap/git-ubuntu/495/usr/lib/python3/dist-packages/gitubuntu/queue.py", line 181, in _get_upload_source_urls
    raise RuntimeError("Cannot find source for %r" % upload)
RuntimeError: Cannot find source for <package_upload at https://api.launchpad.net/devel/ubuntu/xenial/+upload/26047189>

Looks like a case not handled - when a new binary causes an upload to end up in the New queue, it neither contains_source nor contains_copy.