NoMethodError: undefined method `created?' for nil:NilClass

https://sentry.gitlab.net/gitlab/gitlabcom/issues/791372/

NoMethodError: undefined method `created?' for nil:NilClass
  push_event.rb:85:in `new_ref?'
    push_event_payload.created?
  event.rb:376:in `push_action_name'
    if new_ref?
  gitlab/metrics/instrumentation.rb:161:in `block in push_action_name'
    .measure { super }
  gitlab/metrics/method_call.rb:36:in `measure'
    retval = yield
  gitlab/metrics/instrumentation.rb:161:in `push_action_name'
    .measure { super }
...
(150 additional frame(s) were not displayed)

NoMethodError: undefined method `created?' for nil:NilClass