NoMethodError: undefined method `id' for nil:NilClass

https://sentry.gitlab.net/gitlab/gitlabcom/issues/699203/

NoMethodError: undefined method `id' for nil:NilClass
  projects/repository_languages_service.rb:14:in `perform_language_detection'
    ::DetectRepositoryLanguagesWorker.perform_async(project.id, current_user.id)
  gitlab/metrics/instrumentation.rb:161:in `block in perform_language_detection'
    .measure { super }
  gitlab/metrics/method_call.rb:36:in `measure'
    retval = yield
  gitlab/metrics/instrumentation.rb:161:in `perform_language_detection'
    .measure { super }
  projects/repository_languages_service.rb:6:in `execute'
    perform_language_detection unless project.detected_repository_languages?
...
(136 additional frame(s) were not displayed)

NoMethodError: undefined method `id' for nil:NilClass