[null] value test

Hi,

Can someone tell me, how to test null value requirement in the request?[ This is an integer requirement]

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:web="http://www.oorsprong.org/websamples.countryinfo">
<soapenv:Header/>
<soapenv:Body>
<web:CapitalCity>
<web:sCountryISOCode>111</web:sCountryISOCode>
</web:CapitalCity>
</soapenv:Body>
</soapenv:Envelope>

instead of 111, i need to test it with null value. So, possible options are

1. <web:sCountryISOCode>null</web:sCountryISOCode> - null
2. <web:sCountryISOCode>NULL</web:sCountryISOCode> - NULL
3. <web:sCountryISOCode> </web:sCountryISOCode> - space
4. <web:sCountryISOCode>111</web:sCountryISOCode> - remove this node itself and run the request
5. anything else?

Can i have right answer?

^Thanks