protected function strTokenWrapper($string)
    {
        $token = strtok($string, $this->tokenExpression);

        $tokens = array();
        while ($token !== false) {
            // avoid tokenizing white spaces
            if(!empty(trim($token))) { 
                $tokens[] = $token;
            }
            $token = strtok($this->tokenExpression);        
        }
        return $tokens;
    }