zero-length base64 data types in XML-RPC 3?

[Brad Karp]

Greetings.

I'm using Apache XML-RPC 3 to write a Java client that talks to a
server that expects a parameter of type:

 <param><value><base64></base64></value></param>

(That is, a parameter that's of type base64, but zero-length.)

How do I convince XML-RPC 3 to generate that XML output?

I've tried:

        ...
        byte[] pm = "".getBytes();
        ...
        Object[] params = new Object[]{ID, vals, pm, app};
        try {
            Object[] result = (Object[]) client.execute("get", params);
        } catch (org.apache.xmlrpc.XmlRpcException e) {
            ...
        }

But that dies:

Exception in thread "main" java.lang.IllegalArgumentException: The buffer must 
contain at least 4 characters, but has 0
        at org.apache.ws.commons.util.Base64$Encoder.<init>(Base64.java:138)
        at org.apache.ws.commons.util.Base64$SAXEncoder.<init>(Base64.java:300)
        at 
org.apache.xmlrpc.serializer.ByteArraySerializer.write(ByteArraySerializer.java:39)
        at 
org.apache.xmlrpc.serializer.XmlRpcWriter.writeValue(XmlRpcWriter.java:144)
        at org.apache.xmlrpc.serializer.XmlRpcWriter.write(XmlRpcWriter.java:74)
        at 
org.apache.xmlrpc.client.XmlRpcStreamTransport.writeRequest(XmlRpcStreamTransport.java:283)
        at 
org.apache.xmlrpc.client.XmlRpcStreamTransport.sendRequest(XmlRpcStreamTransport.java:207)
        at 
org.apache.xmlrpc.client.XmlRpcClientWorker.execute(XmlRpcClientWorker.java:53)
        at org.apache.xmlrpc.client.XmlRpcClient.execute(XmlRpcClient.java:166)
        at org.apache.xmlrpc.client.XmlRpcClient.execute(XmlRpcClient.java:136)
        at org.apache.xmlrpc.client.XmlRpcClient.execute(XmlRpcClient.java:125)
        at get.main(get.java:32)

Many thanks,
-Brad, [EMAIL PROTECTED]