Merge branch 'sh-fix-error-500-licensee' into 'master'

Fix Error 500s loading repositories with inconsistent HEAD

Closes #43268

See merge request gitlab-org/gitlab-ce!17128

app/models/repository.rb

@@ -593,7 +593,15 @@ class Repository
   def license_key
     return unless exists?
-    Licensee.license(path).try(:key)
+    # The licensee gem creates a Rugged object from the path:
+    # https://github.com/benbalter/licensee/blob/v8.7.0/lib/licensee/projects/git_project.rb
+    begin
+      Licensee.license(path).try(:key)
+    # Normally we would rescue Rugged::Error, but that is banned by lint-rugged
+    # and we need to migrate this endpoint to Gitaly:
+    # https://gitlab.com/gitlab-org/gitaly/issues/1026
+    rescue
+    end
   end
   cache_method :license_key

spec/models/repository_spec.rb

@@ -873,6 +873,18 @@ describe Repository do
       expect(repository.license_key).to be_nil
     end
+    it 'returns nil when the commit SHA does not exist' do
+      allow(repository.head_commit).to receive(:sha).and_return('1' * 40)
+
+      expect(repository.license_key).to be_nil
+    end
+
+    it 'returns nil when master does not exist' do
+      repository.rm_branch(user, 'master')
+
+      expect(repository.license_key).to be_nil
+    end
+
     it 'returns the license key' do
       repository.create_file(user, 'LICENSE',
         Licensee::License.new('mit').content,