diff --git a/include/tool/HTML.php b/include/tool/HTML.php
index 6593f10..7a6b2fc 100644
--- a/include/tool/HTML.php
+++ b/include/tool/HTML.php
@@ -76,7 +76,7 @@ class HTML{
 	}
 
 	public static function Chars($str){
-		return htmlspecialchars($str, ENT_COMPAT, 'UTF-8', false);
+		return htmlspecialchars($str ?? '', ENT_COMPAT, 'UTF-8', false);
 	}