Describe the bug
Error code 55 appears to require that the language in agency.agency_lang matches feed_info.feed_lang. Agency_lang is optional, so this appears to be an erroneous error.

To Reproduce
Run the validator on the following dataset: http://api.511.org/transit/datafeeds?api_key=[key]&operator_id=BA

Expected behavior
No notice should be generated in this case.

Witnessed behavior
This error message was included in the validator results.

Notice{filename='feed_info.txt', level='ERROR', code='55', title='Mismatching feed and agency language fields', description='Agency `agency_name`: `Bay Area Rapid Transit` has mismatching `agency.agency_lang`: `null` and feed_info.feed_lang`: `en`.', extra='{feedInfoFeedLang=en, agencyAgencyLang=null, agencyName=Bay Area Rapid Transit}'}]

Environment used

• OS: macOS Catalina 10.15.6
• Java version: 11.0.5
• gtfs-validator version: v1.2.2

Additional context
None