<?xml version='1.0' encoding='UTF-8'?>
<users>
    <user age="31" dni="30181626">
        <name>Mariano</name>
        <lastName>Achaval</lastName>
        <contacts/>
    </user>
    <user age="33">
        <name>Emiliano</name>
        <lastName>Lesende</lastName>
        <contacts>
            <contact>
                <name>Uri S.</name>
            </contact>
            <contact>
                <name>Dan D.</name>
            </contact>
        </contacts>
    </user>
    <user>
        <name>Luis</name>
        <lastName xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"></lastName>
    </user>
</users>