Setup/UpgradeData.php
private function upgrade1010($newConfigPaths)
    {
        $oldData = $this->scopeConfig->getValue($newConfigPaths['geoip_country_mapping']);
        try {
            $oldData = unserialize($oldData); // @codingStandardsIgnoreLine - used for conversion of old Magento format to json_decode
        } catch (\Exception $e) {
            $oldData = [];
        }
        $oldData = (is_array($oldData)) ? $oldData : [];
        $newData = json_encode($oldData);
        if (false === $newData) {
            throw new \InvalidArgumentException('Unable to encode data.');
        }
        $this->configWriter->save($newConfigPaths['geoip_country_mapping'], $newData);
        $this->cacheManager->clean([\Magento\Framework\App\Cache\Type\Config::TYPE_IDENTIFIER]);
    }
private function upgrade1010($newConfigPaths)
    {
        $oldData = $this->scopeConfig->getValue($newConfigPaths['geoip_country_mapping']);
        try {
            $oldData = unserialize($oldData); // @codingStandardsIgnoreLine - used for conversion of old Magento format to json_decode
        } catch (\Exception $e) {
            $oldData = [];
        }
        $oldData = (is_array($oldData)) ? $oldData : [];
        $newData = json_encode($oldData);
        if (false === $newData) {
            throw new \InvalidArgumentException('Unable to encode data.');
        }
        $this->configWriter->save($newConfigPaths['geoip_country_mapping'], $newData);
        $this->cacheManager->clean([\Magento\Framework\App\Cache\Type\Config::TYPE_IDENTIFIER]);
    }
Convert serialized data to magento supported serialized data
@param $newConfigPaths