How do I delete the value of a custom field (or set it to a null value) through Connect Web Services for SOAP API?

Environment:

All supported versions of Oracle B2C Service and Connect Web Services (CWS) for SOAP API

Resolution:

You might be tempted to try to delete the custom field value by setting it to a null value just like you would set it to any other value. Note that the Connect Web Services for SOAP API has a special procedure for nulling a custom field value.

The following is correct:

     < ns4:CustomFields dataType="STRING" name="c$con_txt">
          < ns2:DataValue xmlns:ns2="urn:generic.ws.rightnow.com/v1_3" xsi:nil="1" />
     < /ns4:CustomFields>

The following syntax is not correct:

     < ns4:CustomFields dataType="STRING" name="c$con_txt">
       < DataValue>
          < StringValue></StringValue>
       < /DataValue>
     < /ns4:CustomFields>

For more information please consult the SOAP API documentation:
Answer ID 5169: Technical Documentation and Sample Code