public function getParameterDescription($parameterName)
    {
        if (!$this->type->hasParameter($parameterName)) {
            throw new NoSuchParameterException(sprintf(
                'The parameter "%s" does not exist.',
                $parameterName
            ));
        }

        if (!isset($this->parameterDescriptions[$parameterName])) {
            throw new OutOfBoundsException(sprintf(
                'No description exists for parameter "%s".',
                $parameterName
            ));
        }

        return $this->parameterDescriptions[$parameterName];
    }