Error 500 when creating merge requests with submodule deletion

This appears to be a similar but different issue to #3893 (closed). When submodules are removed the diff fails to be generated with an error being thrown in submodule_link()

@clausa appears to have the same sort of error as well when renaming a submodule

Started GET "/FooTeam/FooProject/commit/76ed419adc0ee53198cec7b3b8a327ef560f3a7e" for 127.0.0.1 at 2015-12-15 12:00:48 +0000
Processing by Projects::CommitController#show as HTML
  Parameters: {"namespace_id"=>"FooTeam", "project_id"=>"FooProject", "id"=>"76ed419adc0ee53198cec7b3b8a327ef560f3a7e"}
Completed 500 Internal Server Error in 555ms (ActiveRecord: 10.8ms)

ActionView::Template::Error (undefined method `path' for nil:NilClass):
    3:     - if diff_file.diff.submodule?
    4:       %span
    5:         - submodule_item = project.repository.blob_at(@commit.id, diff_file.file_path)
    6:         = submodule_link(submodule_item, @commit.id, project.repository)
    7:     - else
    8:       %span
    9:         - if diff_file.deleted_file
  app/helpers/submodule_helper.rb:6:in `submodule_links'
  app/helpers/diff_helper.rb:161:in `submodule_link'
  app/views/projects/diffs/_file.html.haml:6:in `_app_views_projects_diffs__file_html_haml___2534097047021710941_60536320'
  app/views/projects/diffs/_diffs.html.haml:22:in `block in _app_views_projects_diffs__diffs_html_haml___3790141050834119730_50882100'
  app/views/projects/diffs/_diffs.html.haml:17:in `each'
  app/views/projects/diffs/_diffs.html.haml:17:in `each_with_index'
  app/views/projects/diffs/_diffs.html.haml:17:in `_app_views_projects_diffs__diffs_html_haml___3790141050834119730_50882100'
  app/views/projects/commit/show.html.haml:5:in `_app_views_projects_commit_show_html_haml___4154109768477026444_64730040'
  app/controllers/projects/commit_controller.rb:26:in `show'

--- a/some/foo/dir
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 9f9f65b1c26d9db41cef5ce080a1ce11dee432fa

Added ~12980 label

Milestone changed to 8.4

We should spend some time debugging submodules, it seems.

Milestone changed to 8.3

This is fixed with !1989 (merged) and will be shipped with GitLab 8.3

Status changed to closed

@razer6 @JobV Thank you for the quick response, I'm glad a fix is coming soon!

mentioned in merge request !14785