Maintain "force_remove_source_branch" options on Merge Request unless specified

CHANGELOG

@@ -31,6 +31,7 @@ v 8.13.0 (unreleased)
   - Update Gitlab Shell to fix some problems with moving projects between storages
   - Cache rendered markdown in the database, rather than Redis
   - Avoid database queries on Banzai::ReferenceParser::BaseParser for nodes without references
+  - Do not alter 'force_remove_source_branch' options on MergeRequest unless specified
   - Simplify Mentionable concern instance methods
   - API: Ability to retrieve version information (Robert Schilling)
   - Fix permission for setting an issue's due date

app/services/merge_requests/update_service.rb

@@ -15,7 +15,10 @@ module MergeRequests
         params.except!(:target_branch, :force_remove_source_branch)
       end
 
+      if params[:force_remove_source_branch].present?
         merge_request.merge_params['force_remove_source_branch'] = params.delete(:force_remove_source_branch)
+      end
+
       handle_wip_event(merge_request)
       update(merge_request)
     end

spec/services/merge_requests/update_service_spec.rb

@@ -105,6 +105,18 @@ describe MergeRequests::UpdateService, services: true do
         expect(note).not_to be_nil
         expect(note.note).to eq 'Target branch changed from `master` to `target`'
       end
+
+      context 'when not including source branch removal options' do
+        before do
+          opts.delete(:force_remove_source_branch)
+        end
+
+        it 'maintains the original options' do
+          update_merge_request(opts)
+
+          expect(@merge_request.merge_params["force_remove_source_branch"]).to eq("1")
+        end
+      end
     end
 
     context 'todos' do