Node soap client 调用java webservice 的问题

webservice暴露的接口是getUpcInfo(String barcode),node的代码是这样的:

soapclient = require('soap');
var detailsWsdl = "/home/test/Desktop/upcWsServer.xml";
soapclient.createClient(detailsUrl, function(err, client) {
     client.getUpcInfo({'arg0': '000'}, function(err, result) {
         console.log(result);
     });
});

调用client.describe()的结果是这样的: { input: { arg0: 'xs:string' }, output: { return: 'xs:string' } }

可是webservice接受的参数总是null,各位大大知道问题在哪吗？