diff --git a/app/Services/TG/Hook/Mod/Book.php b/app/Services/TG/Hook/Mod/Book.php
index 2955b603..fae031f7 100644
--- a/app/Services/TG/Hook/Mod/Book.php
+++ b/app/Services/TG/Hook/Mod/Book.php
@@ -899,7 +899,7 @@ class Book extends Base {
         return $this->_rag($iNo, $sRag);
     }
     
-    public function _rag($iNo, $sRag, $mCustom = false)
+    public function _rag($iNo, $sRag, $mCustom = NULL)
     {
         if ($iNo) {
             $oBook = ModelBook::where("path", $this->sPath)->where("no", $iNo)->first();