[Error Budget] Investigate "undefined method `zuora_accound_id`" errors

From #4918 (comment 1124235188)

We're seeing a lot of errors due to undefined method 'zuora_account_id' for nil:NilClass. In the last week we've seen 11.75k events. These errors are contributing significantly to our error budget.

https://sentry.gitlab.net/gitlab/customersgitlabcom/?query=is%3Aunresolved+lastSeen%3A-1w+zuora_account_id