cannot browse files after df36f1f4

cannot browse files after df36f1f4 I/m sure that https://gitlab.com/gitlab-org/gitlab-ce/commit/df36f1f47b7c1dcbe6d34fabd83764ae14919e15#d525ae32a463f9c64367ef9d2c95e4b620817da3 but I cannot help to resolve it.

ActionView::Template::Error (no implicit conversion of nil into String):
    11:       = @project.path
    12:   - path_breadcrumbs do |title, path|
    13:     %li
    14:       = link_to truncate(title, length: 40), namespace_project_tree_path(@project.namespace, @project, tree_join(@ref, path))
    15:
    16:   - if current_user
    17:     %li
  app/helpers/tree_helper.rb:30:in `join'
  app/helpers/tree_helper.rb:30:in `tree_join'
  app/views/projects/tree/_tree_header.html.haml:14:in `block in _app_views_projects_tree__tree_header_html_haml___950746471358799567_47249217245120'
  app/helpers/tree_helper.rb:84:in `path_breadcrumbs'
  app/views/projects/tree/_tree_header.html.haml:12:in `_app_views_projects_tree__tree_header_html_haml___950746471358799567_47249217245120'
  app/views/projects/_files.html.haml:3:in `_app_views_projects__files_html_haml__3578336124716617020_47249217516280'
  app/views/projects/tree/show.html.haml:10:in `_app_views_projects_tree_show_html_haml__164862977890504286_47249223735580'
  app/controllers/projects/tree_controller.rb:27:in `show'
  lib/gitlab/middleware/multipart.rb:93:in `call'
  lib/gitlab/request_profiler/middleware.rb:14:in `call'
  lib/gitlab/middleware/go.rb:16:in `call'
  lib/gitlab/etag_caching/middleware.rb:10:in `call'
  lib/gitlab/request_context.rb:18:in `call'