Fix 500 error on repository settings access when repository is empty

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/27657

app/models/protectable_dropdown.rb

@@ -12,6 +12,8 @@ class ProtectableDropdown
 
   # Tags/branches which are yet to be individually protected
   def protectable_ref_names
+    return [] if @project.empty_repo?
+
     @protectable_ref_names ||= ref_names - non_wildcard_protected_ref_names
   end
 

changelogs/unreleased/fix-500-settings-when-repository-does-not-exist.yml

+---
+title: Fix 500 error on repository settings access when repository is empty
+merge_request: 50844
+author: Diego Louzán
+type: fixed

ee/app/controllers/ee/projects/settings/repository_controller.rb

@@ -5,6 +5,7 @@ module EE
     module Settings
       module RepositoryController
         extend ActiveSupport::Concern
+        extend ::Gitlab::Utils::Override
 
         prepended do
           before_action :push_rule, only: [:show, :create_deploy_token]
@@ -24,7 +25,8 @@ module EE
         end
 
         # rubocop:disable Gitlab/ModuleWithInstanceVariables
-        def acces_levels_options
+        override :access_levels_options
+        def access_levels_options
           super.merge(
             selected_merge_access_levels: @protected_branch.merge_access_levels.map { |access_level| access_level.user_id || access_level.access_level },
             selected_push_access_levels: @protected_branch.push_access_levels.map { |access_level| access_level.user_id || access_level.access_level },

spec/models/protectable_dropdown_spec.rb

@@ -14,21 +14,33 @@ RSpec.describe ProtectableDropdown do
   end
 
   describe '#protectable_ref_names' do
-    before do
-      project.protected_branches.create(name: 'master')
-    end
+    context 'when project repository is not empty' do
+      before do
+        project.protected_branches.create(name: 'master')
+      end
+
+      it { expect(subject.protectable_ref_names).to include('feature') }
+      it { expect(subject.protectable_ref_names).not_to include('master') }
+
+      it "includes branches matching a protected branch wildcard" do
+        expect(subject.protectable_ref_names).to include('feature')
 
-    it { expect(subject.protectable_ref_names).to include('feature') }
-    it { expect(subject.protectable_ref_names).not_to include('master') }
+        create(:protected_branch, name: 'feat*', project: project)
 
-    it "includes branches matching a protected branch wildcard" do
-      expect(subject.protectable_ref_names).to include('feature')
+        subject = described_class.new(project.reload, :branches)
+
+        expect(subject.protectable_ref_names).to include('feature')
+      end
+    end
 
-      create(:protected_branch, name: 'feat*', project: project)
+    context 'when project repository is empty' do
+      let(:project) { create(:project) }
 
-      subject = described_class.new(project.reload, :branches)
+      it "returns empty list" do
+        subject = described_class.new(project, :branches)
 
-      expect(subject.protectable_ref_names).to include('feature')
+        expect(subject.protectable_ref_names).to be_empty
+      end
     end
   end
 end