diff --git a/app/common/service/SubjectHomeworkService.php b/app/common/service/SubjectHomeworkService.php
index bfbad7d..22e0084 100644
--- a/app/common/service/SubjectHomeworkService.php
+++ b/app/common/service/SubjectHomeworkService.php
@@ -120,18 +120,28 @@ class SubjectHomeworkService
 
             if($subject_homework->homework_file_url){
                 $subject_homework->homework_file_url = json_decode($subject_homework->homework_file_url, true);
+            }else{
+                $subject_homework->homework_file_url = [];
             }
             if($subject_homework->homework_version_file_url){
                 $subject_homework->homework_version_file_url = json_decode($subject_homework->homework_version_file_url, true);
+            }else{
+                $subject_homework->homework_version_file_url = [];
             }
             if($subject_homework->last_homework_feedback_url){
                 $subject_homework->last_homework_feedback_url = json_decode($subject_homework->last_homework_feedback_url, true);
+            }else{
+                $subject_homework->last_homework_feedback_url = [];
             }
             if($subject_homework->subject_report_url){
                 $subject_homework->subject_report_url = json_decode($subject_homework->subject_report_url, true);
+            }else{
+                $subject_homework->subject_report_url = [];
             }
             if($subject_homework->subject_file_url){
                 $subject_homework->subject_file_url = json_decode($subject_homework->subject_file_url, true);
+            }else{
+                $subject_homework->subject_file_url = [];
             }
 
             return [