Handle blank default branch in security configuration

ee/app/presenters/projects/security/configuration_presenter.rb

@@ -101,7 +101,7 @@ module Projects
         return '' if project.empty_repo?
 
         gitlab_ci = Gitlab::FileDetector::PATTERNS[:gitlab_ci]
-        Gitlab::Routing.url_helpers.project_blame_path(project, File.join(project.default_branch, gitlab_ci))
+        Gitlab::Routing.url_helpers.project_blame_path(project, File.join(project.default_branch_or_master, gitlab_ci))
       end
 
       def features

ee/changelogs/unreleased/handle-blank-default-branch-in-security-configuration.yml

+---
+title: Use `master` when default branch is blank in security configuration
+merge_request: 48328
+author:
+type: fixed

ee/spec/presenters/projects/security/configuration_presenter_spec.rb

@@ -50,6 +50,16 @@ RSpec.describe Projects::Security::ConfigurationPresenter do
       end
     end
 
+    context 'when the project has no default branch set' do
+      before do
+        allow(project).to receive(:default_branch).and_return(nil)
+      end
+
+      it 'includes the path to gitlab_ci history' do
+        expect(subject[:gitlab_ci_history_path]).to eq(project_blame_path(project, 'master/.gitlab-ci.yml'))
+      end
+    end
+
     context "when the latest default branch pipeline's source is auto devops" do
       before do
         pipeline = create(