ActionView::Template::Error: undefined method `empty?' for nil:NilClass

https://sentry.gitlab.net/gitlab/gitlabcom/issues/3198434/?referrer=gitlab_plugin

NoMethodError: undefined method `empty?' for nil:NilClass
  app/models/broadcast_message.rb:121:in `matches_current_user_access_level?'
    return true if target_access_levels.empty?
  app/models/broadcast_message.rb:88:in `block in fetch_messages'
    message.matches_current_user_access_level?(user_access_level)
  app/models/broadcast_message.rb:87:in `select'
    messages = messages.select do |message|
  app/models/broadcast_message.rb:87:in `fetch_messages'
    messages = messages.select do |message|
  app/models/broadcast_message.rb:48:in `current_notification_messages'
    fetch_messages NOTIFICATION_CACHE_KEY, current_path, user_access_level do
...
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ActionView::Template::Error: undefined method `empty?' for nil:NilClass