NoMethodError: undefined method `[]' for nil:NilClass

https://sentry.gitlab.net/gitlab/gitlabcom/issues/2919694/?referrer=gitlab_plugin

NoMethodError: undefined method `[]' for nil:NilClass
  app/services/error_tracking/collect_error_service.rb:35:in `exception'
    event['exception']['values'].first
  app/services/error_tracking/collect_error_service.rb:10:in `execute'
    name: exception['type'], # Example: ActionView::MissingTemplate
  lib/api/error_tracking/collector.rb:130:in `block in <class:Collector>'
    .execute
  lib/api/api_guard.rb:213:in `call'
    response = super(env)
  lib/gitlab/metrics/elasticsearch_rack_middleware.rb:16:in `call'
    @app.call(env)
...
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