Merge branch '13806-fix' into 'master'

Add nil check for Gitlab.config.prometheus

Closes #13806

See merge request gitlab-org/gitlab-ce!32201

lib/gitlab/database_importers/self_monitoring/project/create_service.rb

@@ -173,7 +173,7 @@ module Gitlab
           end
           def prometheus_enabled?
-            Gitlab.config.prometheus.enable
+            Gitlab.config.prometheus.enable if Gitlab.config.prometheus
           rescue Settingslogic::MissingSetting
             log_error(_('prometheus.enable is not present in gitlab.yml'))
@@ -181,7 +181,7 @@ module Gitlab
           end
           def prometheus_listen_address
-            Gitlab.config.prometheus.listen_address
+            Gitlab.config.prometheus.listen_address if Gitlab.config.prometheus
           rescue Settingslogic::MissingSetting
             log_error(_('prometheus.listen_address is not present in gitlab.yml'))

spec/lib/gitlab/database_importers/self_monitoring/project/create_service_spec.rb

@@ -197,6 +197,17 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
         end
       end
+      context 'when prometheus setting is nil' do
+        before do
+          stub_config(prometheus: nil)
+        end
+
+        it 'does not fail' do
+          expect(result).to include(status: :success)
+          expect(project.prometheus_service).to be_nil
+        end
+      end
+
       context 'when prometheus setting is disabled in gitlab.yml' do
         let(:prometheus_settings) do
           {