public static String getSystemConfig(String propertyName, String defaultValue) {
        final String propertyValue = System.getProperty(propertyName);
        if (defaultValue == null) {
            return propertyValue;
        }

        return propertyValue == null || propertyValue.isEmpty() ? defaultValue : propertyValue;
    }
Gets system property and fall back to the given value as needed.

@param propertyName non-null property name
@param defaultValue default value, only useful if it's not null
@return property value
clickhouse-client/src/main/java/com/clickhouse/client/config/ClickHouseClientOption.java