Merge branch 'fix/cycle-analytics-plan-issue' into 'master'

Fix cycle analytics plan stage when commits are missing

Takes into account when commits are `nil` so the app doesn't throw an exception and also removes them.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/24836

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- 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)
- [x] 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 it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !7694

changelogs/unreleased/fix-cycle-analytics-plan-issue.yml

+---
+title: Fix cycle analytics plan stage when commits are missing
+merge_request: 
+author: 

lib/gitlab/cycle_analytics/base_event.rb

@@ -16,7 +16,7 @@ module Gitlab
 
         event_result.map do |event|
           serialize(event) if has_permission?(event['id'])
-        end
+        end.compact
       end
 
       def custom_query(_base_query); end

lib/gitlab/cycle_analytics/plan_event.rb

@@ -27,6 +27,8 @@ module Gitlab
       end
 
       def first_time_reference_commit(commits, event)
+        return nil if commits.blank?
+
         YAML.load(commits).find do |commit|
           next unless commit[:committed_date] && event['first_mentioned_in_commit_at']
 

spec/lib/gitlab/cycle_analytics/plan_event_spec.rb

@@ -6,5 +6,13 @@ describe Gitlab::CycleAnalytics::PlanEvent do
     it 'has the default order' do
       expect(event.order).to eq(event.start_time_attrs)
     end
+
+    context 'no commits' do
+      it 'does not blow up if there are no commits' do
+        allow_any_instance_of(Gitlab::CycleAnalytics::EventsQuery).to receive(:execute).and_return([{}])
+
+        expect { event.fetch }.not_to raise_error
+      end
+    end
   end
 end