Cannot edit an update that doesn't have bugs using the CLI without providing --bugs

[bowlofeggs]

While testing the second 3.9.0 beta today, I found that I was unable to edit an existing update using the CLI when --bugs was not supplied:

bodhi updates edit --staging --type bugfix FEDORA-2018-a06c4c8780                                                                                                                                                                                                                   
                                                                                                                                                                                                                                             
Warning: url and staging flags are both set. url will be ignored.
                                                                                                                                                                                                                                             
Unable to create update.  'NoneType' object is not iterable

On the server side, I found this traceback:

[Tue Jul 31 17:35:26.828765 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] 2018-07-31 17:35:26,828 DEBUG [bodhi.server][Dummy-4] validated = {'close_bugs': False, 'stable_karma': 1, 'csrf_token': u'c766bf3474040a2cbce8f48988fac3b9f82e90ae', 'requirements': None, 'builds': [u'python-rpdb-0.1.6-7.fc27'], 'autokarma': False, 'edited': u'python-rpdb-0.1.6-7.fc27', 'suggest': <unspecified>, 'notes': u'Test', 'request': <testing>, 'bugs': None, 'unstable_karma': -3, 'require_bugs': True, 'require_testcases': True, 'type': <bugfix>, 'severity': <unspecified>}
[Tue Jul 31 17:35:27.062162 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] 2018-07-31 17:35:27,062 INFO  [bodhi.server][Dummy-4] Editing update: python-rpdb-0.1.6-7.fc27
[Tue Jul 31 17:35:27.533548 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] 2018-07-31 17:35:27,533 INFO  [bodhi.server][Dummy-4] Sending mail to rbarlow@redhat.com: [Fedora Update] [comment] python-rpdb-0.1.6-7.fc27
[Tue Jul 31 17:35:27.533921 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] 2018-07-31 17:35:27,533 INFO  [bodhi.server][Dummy-4] Not sending email: No smtp_server defined
[Tue Jul 31 17:35:27.535163 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] 2018-07-31 17:35:27,534 ERROR [bodhi.server][Dummy-4] Failed to create update
[Tue Jul 31 17:35:27.535243 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] Traceback (most recent call last):
[Tue Jul 31 17:35:27.535306 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288]   File "/usr/lib/python2.7/site-packages/bodhi/server/services/updates.py", line 504, in new_update
[Tue Jul 31 17:35:27.535367 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288]     result, _caveats = Update.edit(request, data)
[Tue Jul 31 17:35:27.535427 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288]   File "/usr/lib/python2.7/site-packages/bodhi/server/models.py", line 2193, in edit
[Tue Jul 31 17:35:27.535487 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288]     new_bugs = up.update_bugs(data['bugs'], db)
[Tue Jul 31 17:35:27.535588 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288]   File "/usr/lib/python2.7/site-packages/bodhi/server/models.py", line 2911, in update_bugs
[Tue Jul 31 17:35:27.535677 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288]     for bug_id in bug_ids:
[Tue Jul 31 17:35:27.535744 2018] [wsgi:error] [pid 12:tid 140210130114304] [client 10.130.0.1:35288] TypeError: 'NoneType' object is not iterable

I am able to use the web UI to edit the same update without adding bugs to it.