Error 500 when access a part of wikis

Parameters: {"namespace_id"=>"docs", "project_id"=>"simple", "id"=>"reference/simple-reference"} Completed 500 Internal Server Error in 65ms (ActiveRecord: 5.4ms | Elasticsearch: 0.0ms)

ActionView::Template::Error (undefined method author_name' for nil:NilClass): 11: .nav-text 12: %h2.wiki-page-title= @page.title.capitalize 13: %span.wiki-last-edit-by 14: = (_("Last edited by %{name}") % { name: "<strong>#{@page.last_version.author_name}</strong>" }).html_safe 15: #{time_ago_with_tooltip(@page.last_version.authored_date)} 16: 17: .nav-controls app/views/projects/wikis/show.html.haml:14:in _app_views_projects_wikis_show_html_haml___734797160828825150_70278656450700' app/controllers/projects/wikis_controller.rb:18:in show' lib/gitlab/i18n.rb:47:in with_locale' lib/gitlab/i18n.rb:53:in with_user_locale' app/controllers/application_controller.rb:332:in set_locale' lib/gitlab/middleware/multipart.rb:93:in call' lib/gitlab/request_profiler/middleware.rb:14:in call' lib/gitlab/jira/middleware.rb:15:in call' lib/gitlab/middleware/go.rb:18:in call' lib/gitlab/etag_caching/middleware.rb:11:in call' lib/gitlab/middleware/read_only.rb:31:in call' lib/gitlab/request_context.rb:18:in call' lib/gitlab/metrics/requests_rack_middleware.rb:27:in call'