[variant_expiration] ParserError: Unknown string format: None

[sentry]

Sentry Issue: BUGBOT-42

ParserError: Unknown string format: None
(3 additional frame(s) were not displayed)
...
  File "variant_expiration.py", line 445, in <module>
    VariantExpiration().run()
  File "variant_expiration.py", line 101, in __init__
    self.variants = self.get_variants()
  File "variant_expiration.py", line 149, in get_variants
    variant["expiration"] = lmdutils.get_date_ymd(expiration)

Uncaught exception