```ruby
class TimelineManager
  include BackgroundJob

  # Find the post author's local followers and add the post
  # to each of their timelines.
  #
  def add_post_to_local_timelines(post)
    with_database do
      post.user.followers.hosted.find_each do |follower|
        follower.add_to_timeline(post)
      end
    end
  end
end
```

Fix TimelineManager to check if the given post and its user are present before doing its thing.
user
```ruby
class TimelineManager
  include BackgroundJob

  # Find the post author's local followers and add the post
  # to each of their timelines.
  #
  def add_post_to_local_timelines(post)
    with_database do
      if post.try(:user).present?
        post.user.followers.hosted.find_each do |follower|
          follower.add_to_timeline(post)
        end
      end
    end
  end
end
```
assistant