RepositoryUpdateMirrorWorker returns undefined method `[]' for false:FalseClass

/cc: @jameslopez

https://sentry.gitlap.com/gitlab/gitlabcom/issues/88/

NoMethodError: undefined method `[]' for false:FalseClass
  app/workers/repository_update_mirror_worker.rb:18:in `perform'
    if result[:status] == :error
  lib/gitlab/sidekiq_middleware/memory_killer.rb:17:in `call'
    yield
  lib/gitlab/sidekiq_middleware/arguments_logger.rb:6:in `call'
    yield
  lib/gitlab/metrics/sidekiq_middleware.rb:11:in `block in call'
    trans.run { yield }
  lib/gitlab/metrics/transaction.rb:45:in `run'
    yield
...
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