Thanks again for your help, this is very frustrating.
I made this change
<serviceTask id="_11" name="Evaluate Score" operationRef="_11_ServiceOperation" implementation="Other" >
<ioSpecification>
<dataInput id="_11_varsInput" name="Parameter" />
<dataOutput id="_11_varsOutput" name="Result" />
But the parameter is still null in my service task method. BPMN2-ServiceProcess and its jUnit test testServiceTask() show no other references to "Parameter" so I didn't change anything else.
Also ServiceTaskHandler doesn't provide a getter for workItem so I don't see how to debug or call
public class ServiceTaskHandler implements WorkItemHandler {
public void executeWorkItem(WorkItem workItem, WorkItemManager manager)