TypeError: no implicit conversion of nil into String

[irees]

https://sentry.io/mapzen/datastore-prod/issues/195808529/

TypeError: no implicit conversion of nil into String
  app/services/feed_fetcher_service.rb:151:in `read_gtfs_info'
    start_date, end_date = gtfs.service_period_range
  app/services/feed_fetcher_service.rb:144:in `fetch_and_normalize_feed_version'
    data = data.merge!(read_gtfs_info(gtfs))
  app/services/feed_fetcher_service.rb:54:in `fetch_and_return_feed_version'
    feed_version = fetch_and_normalize_feed_version(feed)
  app/workers/feed_fetcher_worker.rb:11:in `perform'
    feed_version = FeedFetcherService.fetch_and_return_feed_version(feed)
...
(36 additional frame(s) were not displayed)

TypeError: no implicit conversion of nil into String

[drewda]

https://sentry.io/mapzen/datastore-prod/issues/298654569/

[drewda]

https://sentry.io/mapzen/datastore-prod/issues/246861557/

[drewda]

One instance of this happening:

• Dispatcher: https://transit.land/dispatcher/feeds/f-9y68-clevelandarearapidtransitcart
• remote feed URL: http://www.cartgps.com/gtfs

The zip file that is currently served includes many empty files:

I've just contacted CART to see if they have a current GTFS feed at a new location.

We may also want to consider throwing a more descriptive error about missing calendars in the future -- as well as catching it more gracefully, so it doesn't have to go all the way to Sentry.