Unable to schema validate the xml node created from SOAP Message having xsi:nil.

I am sending a SOAP request Message which is containing xsi:nil=“true” in one of the elements whose data type is String. In my web Service I am converting this message into an xml node and validating it against a schema in which nillable property of that element is set to true. But I am getting schema validation error saying that " value does not conform to data type" for that element.

The webmethods version I am using is :
[TABLE=“class: tableView, width: 100%”]
[TD=“class: evenrow”]Version[/TD]
[TD=“class: evenrowdata-l”][/TD]
[TD=“class: oddrow”]Updates[/TD]
[TD=“class: oddrowdata-l”]IS_8.2_SP2_Core_Fix4. [/TD]
In extended properties I have also given :
When I am converting the Soap request into XML string the element having xsi:nil=“true” is converted into an xml element with blank value.

<soapenv:Envelope xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance” xmlns:soapenv=“http://schemas.xmlsoap.org/soap/envelope/

                  <ns:DCMinimumShelfLife xsi:nil="true"></ns:DCMinimumShelfLife>


Corresponding XML String:

<?xml version="1.0" versionID="" systemEnvironmentCode=""?>