Merge branch 'feature/exam' into dev

合并冲突

src/Hotline.Application/Exam/Service/Questions/QuestionService.cs

@@ -980,7 +980,7 @@ namespace Hotline.Application.Exam.Service.Questions
 
             var questionAnswerDto = _mapper.Map<QuestionAnswerDto>(questionAnswer);
 
-            return questionAnswerDto;
+            return questionAnswerDto ?? new QuestionAnswerDto();
         }
 
         private async Task<List<QuestionTagDto>> GetQuestionTags(EntityQueryRequest entityQueryRequest)