check_url_dupe exception

Production through this exception twice as someone tried to submit a story. I've redacted a couple form values with ... but they weren't in any way unusual.

An ActionView::Template::Error occurred in stories#check_url_dupe:

  undefined method `created_at' for nil:NilClass
  app/views/stories/_form_errors.html.erb:7:in `_app_views_stories__form_errors_html_erb___2969812256811510683_64400'


-------------------------------
Request:
-------------------------------

  * URL        : https://lobste.rs/stories/check_url_dupe
  * HTTP Method: POST
  * Parameters : {"utf8"=>"✓",
"authenticity_token"=>"...",
"story"=>{"url"=>"...", "title"=>"...", "tags_a"=>["",
"practices"], "description"=>"", "user_is_author"=>"0", "user_is_following"=>"1"}, "controller"=>"stories",
"action"=>"check_url_dupe"}
  * Server : lobsters
    * Rails root : /srv/lobste.rs/http
  * Process: 1018232


    app/views/stories/_form_errors.html.erb:7:in `_app_views_stories__form_errors_html_erb___2969812256811510683_64400'
    app/controllers/stories_controller.rb:363:in `block (2 levels) in check_url_dupe'
    app/controllers/stories_controller.rb:361:in `check_url_dupe'
    config/initializers/production.rb:42:in `call'