protected function getDateFormat(PropertyMappingConfigurationInterface $configuration = null)
    {
        if ($configuration === null) {
            return self::DEFAULT_DATE_FORMAT;
        }

        $dateFormat = $configuration->getConfigurationValue(StringConverter::class, self::CONFIGURATION_DATE_FORMAT);
        if ($dateFormat === null) {
            return self::DEFAULT_DATE_FORMAT;
        } elseif ($dateFormat !== null && !is_string($dateFormat)) {
            throw new InvalidPropertyMappingConfigurationException('CONFIGURATION_DATE_FORMAT must be of type string, "' . (is_object($dateFormat) ? get_class($dateFormat) : gettype($dateFormat)) . '" given', 1404229004);
        }

        return $dateFormat;
    }