TypeError: Parser must be a string or character stream, not NoneType

[sentry]

Sentry Issue: BUGBOT-52

TypeError: Parser must be a string or character stream, not NoneType
(17 additional frame(s) were not displayed)
...
  File "bugbot/bzcleaner.py", line 712, in get_email_data
    bugs = self.get_bugs(date=date)
  File "patch_closed_bug.py", line 44, in get_bugs
    bugs = super().get_bugs(date, bug_ids, chunk_size)
  File "bugbot/bzcleaner.py", line 486, in get_bugs
    ).get_data().wait()
  File "bugbot/bzcleaner.py", line 362, in bughandler
    if self.handle_bug(bug, data) is None:
  File "patch_closed_bug.py", line 67, in handle_bug
    resolved_at = parser.parse(bug["cf_last_resolved"])

Rule patch_closed_bug