Fix undefined property sign

1 files changed, 1 insertions, 0 deletions

diff --git a/parser.php b/parser.php
index 4a37832..c87ef64 100644
--- a/parser.php
+++ b/parser.php
@@ -1306,6 +1306,7 @@ class qtype_algebra_parser_bracket extends qtype_algebra_parser_term {
 
     function __construct($text) {
         parent::__construct(self::NARGS,self::$formats[$text],$text);
+        $this->_sign=''; 
         $this->_open=$text;
         switch($this->_open) {
             case '(':