public function getVersion()
    {
        if (!array_key_exists(self::VERSION_KEY, $this->data)) {
            $this->data[self::VERSION_KEY] = self::MINIMUM_VERSION;
        }

        if (!version_compare($this->data[self::VERSION_KEY], SwaggerParser::MINIMUM_VERSION, '>=')) {
            throw new InvalidVersionException($this->data[self::VERSION_KEY]);
        }

        return $this->data[self::VERSION_KEY];
    }