build_hash failure on None mozlint check

[La0]

https://sentry.prod.mozaws.net/operations/code-review-bot/issues/6465123/

TypeError: sequence item 3: expected str instance, NoneType found
(4 additional frame(s) were not displayed)
...
  File "code_review_bot/workflow.py", line 122, in publish
    reporter.publish(issues, revision)
  File "code_review_bot/report/debug.py", line 47, in publish
    "issues": [issue.as_dict() for issue in issues],
  File "code_review_bot/report/debug.py", line 47, in <listcomp>
    "issues": [issue.as_dict() for issue in issues],
  File "code_review_bot/__init__.py", line 199, in as_dict
    "hash": self.build_hash(),
  File "code_review_bot/__init__.py", line 146, in build_hash
    payload = ":".join(

TypeError: sequence item 3: expected str instance, NoneType found

[La0]

This happens on licence checks from mozlint: source-test-mozlint-license issue None@error intl/locale/rust/unic-langid-ffi/src/lib.rs line 0