public function getDefaultValue()
    {
        if ($this->isDefaultValueAvailable()) {
            $prettyPrinter = new PrettyPrinter\Standard;
            return $prettyPrinter->prettyPrintExpr($this->node->default);
        }
        throw new ModelException(
            sprintf(
                'Parameter #%d [$%s] is not optional.',
                $this->getPosition(),
                $this->getName()
            )
        );
    }