Errore di Undefined variable

[crycrycry]

Notice: Undefined variable: hrefVars in c:\programmi\easyphp1-8\www\planet2\components\com_mambelfish\mambelfish .html.php on line 154

Notice: Undefined variable: hrefVars in c:\programmi\easyphp1-8\www\planet2\components\com_mambelfish\mambelfish .html.php on line 154

Notice: Undefined variable: hrefVars in c:\programmi\easyphp1-8\www\planet2\components\com_mambelfish\mambelfish .html.php on line 154

Notice: Undefined variable: hrefVars in c:\programmi\easyphp1-8\www\planet2\components\com_mambelfish\mambelfish .html.php on line 154


Le righe di codice sono:

         if( $iso != null ) {
            if( $hrefVars != "" ) $hrefVars .= "&";
            $hrefVars .= "lang=$iso"; 

come lo risolvo?