500 Errors in todo list after 8.15 update

Summary

Some of our users are unable to get to their todo list after we updated our server to 8.15.

Steps to reproduce

Tried impersonating users and checking their todo list as admin. Only happening with 3 of our users.

Expected behavior

Todo list page

Actual behavior

serves 500 error

Relevant logs and/or screenshots

gitlab_1  | Started GET "/dashboard/todos" for 172.xx.x.x at 2016-12-22 23:23:35 +0000
gitlab_1  | Processing by Dashboard::TodosController#index as HTML
gitlab_1  | Completed 500 Internal Server Error in 203ms (ActiveRecord: 9.1ms)
gitlab_1  |
gitlab_1  | ActionView::Template::Error (undefined method `builds_namespace_project_merge_request_path' for #<#<Class:0x007f8becea9398>:0x007f8bec728b78>
gitlab_1  | Did you mean?  diffs_namespace_project_merge_request_path
gitlab_1  |                builds_namespace_project_pipeline_url
gitlab_1  |                builds_namespace_project_pipeline_path
gitlab_1  |                diffs_namespace_project_merge_request_url
gitlab_1  |                build_namespace_project_badges_path
gitlab_1  |                build_namespace_project_badges_url
gitlab_1  |                bulk_update_namespace_project_merge_requests_path):
gitlab_1  |     1: %li{class: "todo todo-#{todo.done? ? 'done' : 'pending'}", id: dom_id(todo), data:{url: todo_target_path(todo)} }
gitlab_1  |     2:   = author_avatar(todo, size: 40)
gitlab_1  |     3:
gitlab_1  |     4:   .todo-item.todo-block
gitlab_1  |   app/helpers/todos_helper.rb:40:in `todo_target_path'
gitlab_1  |   app/views/dashboard/todos/_todo.html.haml:1:in `_app_views_dashboard_todos__todo_html_haml__337834055036405493_70119478711860'
gitlab_1  |   app/views/dashboard/todos/index.html.haml:80:in `block in _app_views_dashboard_todos_index_html_haml__3305903187851727661_70119465276340'
gitlab_1  |   app/views/dashboard/todos/index.html.haml:73:in `each'
gitlab_1  |   app/views/dashboard/todos/index.html.haml:73:in `_app_views_dashboard_todos_index_html_haml__3305903187851727661_70119465276340'
gitlab_1  |   lib/gitlab/middleware/multipart.rb:93:in `call'
gitlab_1  |   lib/gitlab/request_profiler/middleware.rb:15:in `call'
gitlab_1  |   lib/gitlab/middleware/go.rb:16:in `call'
gitlab_1  |   lib/gitlab/middleware/readonly_geo.rb:29:in `call'
gitlab_1  |
gitlab_1  |
gitlab_1  |
gitlab_1  | ==> /var/log/gitlab/gitlab-workhorse/current <==
gitlab_1  | 2016-12-22_23:23:35.60556 2016/12/22 23:23:35 ErrorPage: serving predefined error page: 500
gitlab_1  | 2016-12-22_23:23:35.60584 gitlab.xxx.com @ - - [2016-12-22 23:23:35.397966999 +0000 UTC] "GET /dashboard/todos HTTP/1.1" 500 2648 "" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.95 Safari/537.36" 0.207745```

AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.95 Safari/537.36" 0.207745
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