If a private change merges, the event is still broadcast over the event stream and connected webhooks. At present, the cherry-pick bot reasonably assumes that if an event for a change is received, the relevant change exists.

Unfortunately, this means that when Gerrit returns a 404 Not Found error for a private change, the error goes unhandled and the bot crashes.

404's should be handled gracefully with logged errors, but should never crash the bot.