Error: Processing by AccountsController#public as HTML

gistfile1.txt

Rendered projects/_expand_ideation_processes_list.html.haml (15.7ms)
Rendered projects/_project.html.haml (159.9ms)
Rendered projects/_projects.html.haml (167.7ms)
Rendered accounts/public.html.haml within layouts/yutongo (170.0ms)
Completed 500 Internal Server Error in 174ms

ActionView::Template::Error (undefined method `html_safe' for nil:NilClass):
    46:                     %a.toggle-play-process.btn.red-button.shadow-btn{:href => play_ideation_process_path(ideation_process)}= t(".play", :default => "Play")
    47:                 - else
    48:                   = show_invite_button(ideation_process, :class => "btn red-button shadow-btn", :start_label => "Start").html_safe
    49:               - else
    50:                 %a.btn.red-button.shadow-btn{:href => login_path(project, :return_to => request.fullpath)} Apply
  app/views/projects/_expand_ideation_processes_list.html.haml:49:in `block in _app_views_projects__expand_ideation_processes_list_html_haml__3137288355304606999_58954380'