Why is it that when I populate a webService with certain fields that are required, the ones that are nillable show up as ?

I am working with a WSDL and schema that was provided to me and some of the fields are "nilllable" so I don't populate them.  When I capture the output from the execution of the WebService (SOAP) it always puts the tag and xsi:null="true" in the xml instead of just not showing the tag.  How can I get it so that it won't show the tag if it's empty and/or null.