fix the merger override to remove source branch

app/services/merge_requests/merge_service.rb

@@ -60,13 +60,11 @@ module MergeRequests
     def after_merge
       MergeRequests::PostMergeService.new(project, current_user).execute(merge_request)
-      if params[:should_remove_source_branch].present? || @merge_request.force_remove_source_branch?
+      if delete_source_branch?
         # Verify again that the source branch can be removed, since branch may be protected,
         # or the source branch may have been updated.
-        if @merge_request.can_remove_source_branch?(branch_deletion_user)
-          DeleteBranchService.new(@merge_request.source_project, branch_deletion_user)
-            .execute(merge_request.source_branch)
-        end
+        DeleteBranchService.new(@merge_request.source_project, branch_deletion_user)
+          .execute(merge_request.source_branch)
       end
     end
@@ -78,6 +76,11 @@ module MergeRequests
       @merge_request.force_remove_source_branch? ? @merge_request.author : current_user
     end
+    def delete_source_branch?
+      params.fetch('should_remove_source_branch', @merge_request.force_remove_source_branch?) &&
+        @merge_request.can_remove_source_branch?(branch_deletion_user)
+    end
+
     # Logs merge error message and cleans `MergeRequest#merge_jid`.
     #
     def handle_merge_error(log_message:, save_message_on_model: false)