Fix and relevant spec for plan stage breaking with nil commits

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