调整

app/views/examination_banks/show.json.jbuilder

@@ -40,8 +40,10 @@ json.exam do
   json.all_questions_count @items.size
 
   json.discipline do
+    if @exam.sub_discipline&.discipline.present?
       json.(@exam.sub_discipline&.discipline, :id, :name)
     end
+  end
   json.sub_discipline do
     json.(@exam.sub_discipline, :id, :name)
   end