The scenario - Check whether the optional Title element is present in the input XML payload to the BPEL process. If it isn't present, then add it with the default value "DefaultValue".
The XSD -
The input XML -
I created a simple synchronous BPEL process with input and output variable set to outputCustomerData. I added a transform activity.
The following will check whether the element is present and set the default value, if necessary.