Handle nil descriptions in Slack issue messages

Closes #14676

CHANGELOG

@@ -6,6 +6,7 @@ v 8.7.0 (unreleased)
   - Make HTTP(s) label consistent on clone bar (Stan Hu)
   - Fix avatar stretching by providing a cropping feature
   - Add links to CI setup documentation from project settings and builds pages
+  - Handle nil descriptions in Slack issue messages (Stan Hu)
   - Implement 'Groups View' as an option for dashboard preferences !3379 (Elias W.)
   - Implement 'TODOs View' as an option for dashboard preferences !3379 (Elias W.)
 

app/models/project_services/slack_service/issue_message.rb

@@ -22,7 +22,7 @@ class SlackService
       @issue_url = obj_attr[:url]
       @action = obj_attr[:action]
       @state = obj_attr[:state]
-      @description = obj_attr[:description]
+      @description = obj_attr[:description] || ''
     end
 
     def attachments

spec/models/project_services/slack_service/issue_message_spec.rb

@@ -27,6 +27,16 @@ describe SlackService::IssueMessage, models: true do
 
   let(:color) { '#345' }
 
+  context '#initialize' do
+    before do
+      args[:object_attributes][:description] = nil
+    end
+
+    it 'returns a non-null description' do
+      expect(subject.description).to eq('')
+    end
+  end
+
   context 'open' do
     it 'returns a message regarding opening of issues' do
       expect(subject.pretext).to eq(