[Multiple Issue Assignees] Fix of issues export[ci skip]

app/services/issues/export_csv_service.rb

@@ -21,7 +21,7 @@ module Issues
 
     def csv_builder
       @csv_builder ||=
-        CsvBuilder.new(@issues.includes(:author, :assignee), header_to_value_hash)
+        CsvBuilder.new(@issues.includes(:author, :assignees), header_to_value_hash)
     end
 
     private
@@ -35,8 +35,8 @@ module Issues
        'Description' => 'description',
        'Author' => 'author_name',
        'Author Username' => -> (issue) { issue.author&.username },
-       'Assignee' => 'assignee_name',
-       'Assignee Username' => -> (issue) { issue.assignee_list },
+       'Assignee' => -> (issue) { issue.assignees.pluck(:name).join(', ') },
+       'Assignee Username' => -> (issue) { issue.assignees.pluck(:username).join(', ') },
        'Confidential' => -> (issue) { issue.confidential? ? 'Yes' : 'No' },
        'Due Date' => -> (issue) { issue.due_date&.to_s(:csv) },
        'Created At (UTC)' => -> (issue) { issue.created_at&.to_s(:csv) },

spec/services/issues/export_csv_service_spec.rb

@@ -33,7 +33,7 @@ describe Issues::ExportCsvService, services: true do
 
     before do
       issue.update!(milestone: milestone,
-                    assignee: user,
+                    assignees: [user],
                     description: 'Issue with details',
                     state: :reopened,
                     due_date: DateTime.new(2014, 3, 2),
@@ -71,11 +71,11 @@ describe Issues::ExportCsvService, services: true do
     end
 
     specify 'assignee name' do
-      expect(csv[0]['Assignee']).to eq issue.assignee_name
+      expect(csv[0]['Assignee']).to eq user.name
     end
 
     specify 'assignee username' do
-      expect(csv[0]['Assignee Username']).to eq issue.assignee.username
+      expect(csv[0]['Assignee Username']).to eq user.username
     end
 
     specify 'confidential' do