Merge branch '22246-actionview-template-error-undefined-method-each-for-nil-nilclass' into 'master'

MergeRequest#environments now returns an empty array when diff_head_commit is nil

## Does this MR meet the acceptance criteria?

- [x] No CHANGELOG needed for a bug introduced in an RC.
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #22246

See merge request !6379

1 files changed, 1 insertions, 1 deletions

diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index f7d1253d957..75f48fd4ba5 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -652,7 +652,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def environments
-    return unless diff_head_commit
+    return [] unless diff_head_commit
 
     target_project.environments.select do |environment|
       environment.includes_commit?(diff_head_commit)