private static void addIfNotNull(XmlWriter xml, String xmlTag, Object value) {
        if (value != null && value.toString() != null) {
            xml.start(xmlTag).value(value.toString()).end();
        }
    }
Converts the SelectObjectContentRequest to an XML fragment that can be sent to
the SelectObjectContent operation of Amazon S3.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/transform/RequestXmlFactory.java