problem with Hashtable as return value of XmlRpc calls

[Biermann, Sylvia]

Hello,
 
my question is, if it is possible to have an java.util.Hashtable as the
return value of a XmlRpc call. 
I tried it, but I have got a java.lang.NullPointerException as return
value.
 
This is my code:
 
The server:
private WebServer server; 
server = new WebServer(portNumber);
server.addHandler("$default", this); 
server.start(); 
 
The method to invoke:
public Hashtable displayDriverStarted(String displayID) {
  ... 
  Hashtable resultTable = new Hashtable();
  ...
  resultTable.put("isOk",new Boolean(response.Ok()));
  resultTable.put("errorText",response.Error());
  return resultTable; 
 }
 
The client side:
 
private XmlRpcClient client;
client = new XmlRpcClient("http://"; + this.serverIPAddress + ":" +
serverPortNumber + "/RPC2"); 
 
...
Object returnObject = null;
returnObject = client.execute("displayDriverStarted", params);
try{
   responseTable = (Hashtable) returnObject;
   isOk = ((Boolean)(responseTable.get("isOk"))).booleanValue();
   errorText = (String)responseTable.get("errorText");
  }
  catch (Exception e){
   logger.error("Unaspected return value: " + returnObject);
  }
 
While debugging I realized that in org.apache.xmlrpc.Invoker in method
execute(String methodName, Vector params) the instruction
returnValue = method.invoke(invokeTarget, argValues);
throws a InvocationTargetException.
 
Is there a solution for this problem?
 
Thanks,
Sylvia Biermann