diff --git a/app/Http/Controllers/Admin/CourseContentController.php b/app/Http/Controllers/Admin/CourseContentController.php
index 1484b27..ddd85cc 100755
--- a/app/Http/Controllers/Admin/CourseContentController.php
+++ b/app/Http/Controllers/Admin/CourseContentController.php
@@ -82,7 +82,7 @@ class CourseContentController extends BaseController
                         }
                         // null搜索
                         if ($op == 'null') {
-                            $query->whereNull($key)->orWhereRaw('json_length(' . $key . ') =', 0);
+                            $query->whereNull($key)->orWhereRaw("json_length($key) = 0");
                         }
                         // notnull搜索
                         if ($op == 'notnull') {