xfire怎么传递流类型参数？？？

我创建了一个xfire webservice方法public String imageScan(ZipInputStream zis)我创建client客户端的时候
FileInputStream ips = new FileInputStream(new File("F:/62011140000113510_1.zip"));
ZipInputStream zis = new ZipInputStream(ips);Client client = new Client(new URL(serviceUrl));
Object[] results = client.invoke("imageScan", new Object[] {zis });
result = (String) results[0];报空指针错误。
现在确定为zis这个参数的问题。我想问下xfire怎么传递文件流参数不出问题呢？？xfire支持流参数类型吗？？错误信息如下org.codehaus.xfire.fault.XFireFault: Fault: java.lang.NullPointerException
at org.codehaus.xfire.fault.XFireFault.createFault(XFireFault.java:89)
at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:83)
at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:114)
at org.codehaus.xfire.client.Client.invoke(Client.java:336)
at org.codehaus.xfire.client.Client.invoke(Client.java:368)
at com.sunyard.insurance.ecm.webservice.client.ImageScanServiceClient.scan(ImageScanServiceClient.java:22)
at com.sunyard.insurance.ecm.webservice.client.ImageScanServiceClient.main(ImageScanServiceClient.java:36)
Caused by: java.lang.NullPointerException
at org.codehaus.xfire.aegis.type.basic.ObjectType.writeObject(ObjectType.java:192)
at org.codehaus.xfire.aegis.AegisBindingProvider.writeParameter(AegisBindingProvider.java:229)
at org.codehaus.xfire.service.binding.AbstractBinding.writeParameter(AbstractBinding.java:273)
at org.codehaus.xfire.service.binding.WrappedBinding.writeMessage(WrappedBinding.java:90)
at org.codehaus.xfire.soap.SoapSerializer.writeMessage(SoapSerializer.java:80)
at org.codehaus.xfire.transport.http.HttpChannel.writeWithoutAttachments(HttpChannel.java:56)
at org.codehaus.xfire.transport.http.CommonsHttpMessageSender.getByteArrayRequestEntity(CommonsHttpMessageSender.java:422)
at org.codehaus.xfire.transport.http.CommonsHttpMessageSender.send(CommonsHttpMessageSender.java:360)
at org.codehaus.xfire.transport.http.HttpChannel.sendViaClient(HttpChannel.java:123)
at org.codehaus.xfire.transport.http.HttpChannel.send(HttpChannel.java:48)
at org.codehaus.xfire.handler.OutMessageSender.invoke(OutMessageSender.java:26)
at org.codehaus.xfire.handler.HandlerPipeline.invoke(HandlerPipeline.java:131) at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:79)
... 5 more