private function parameter($name)
    {
        $parameters = $this->parameters();
        if (!isset($parameters[$name])) {
            throw new Exception("Signature parameters does not contain '$name'");
        }

        return $parameters[$name];
    }
private function parameter($name)
    {
        $parameters = $this->parameters();
        if (!isset($parameters[$name])) {
            throw new Exception("Signature parameters does not contain '$name'");
        }

        return $parameters[$name];
    }
@param string $name

@return string

@throws Exception