public void runZipCode() throws Exception {
  // create an execution engine
    exec = OWLSFactory.createExecutionEngine();
      // create a kb
   OWLKnowledgeBase kb = OWLFactory.createKB();
          // read in the service description
   Service aService = kb.readService("file:///f:/proTest/protege/OWL-S_Protege/sayHello_withParam.owl");
   // get the process for the server
   Process aProcess = aService.getProcess();
   
   // initialize the input values to be empty
   ValueMap aInputValueMap = new ValueMap();
   
   // specify an input value
   String inValue = "good";
   // set the value in the map
   aInputValueMap.setDataValue(aProcess.getInput("InputString"), inValue);
           
   // run the process
   ValueMap aOutputValueMap = exec.execute(aProcess, aInputValueMap);  
   
   // get the output
   OWLDataValue out = (OWLDataValue) aOutputValueMap.getValue(aProcess.getOutput());

   // display the value
   System.err.println("Output = "+out.getValue());
 }

运行后出现如下错误，请问如何解决，或许我这样做是不对的？

java.lang.NullPointerException: ValueMap cannot set a value for null variable
       at org.mindswap.query.ValueMap.setValue(ValueMap.java:77)
       at org.mindswap.query.ValueMap.setDataValue(ValueMap.java:67)
       at HelloWorld.runZipCode(HelloWorld.java:120)
       at HelloWorld.main(HelloWorld.java:369)

这句的 InputString 错了