WSO2 PayloadFactory介体空参数

在我的WSO2 ESB 4.7.0中我配置了这个代理：

<proxy xmlns="http://ws.apache.org/ns/synapse" name="SendingByJmsAddressProxy"
     transports="https,http"
     statistics="disable"
     trace="disable"
     startOnLoad="true">
 <target>
    <inSequence>
       <send>
          <endpoint>
             <address uri="http://localhost:8080/RestService/rest/servizio"/>
          </endpoint>
       </send>
    </inSequence>
    <outSequence>
       <log>
          <property name="codice" expression="//codice"/>
       </log>
       <log level="full"/>
       <switch source="//codice">
          <case regex="asd">
             <send/>
          </case>
          <case regex="0">
             <log>
                <property name="codice" value="check1"/>
             </log>
             <send/>
             <payloadFactory media-type="xml">
                <format>
                   <code>$1</code>
                </format>
                <args>
                   <arg xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope" evaluator="xml"
                        expression="//codice"/>
                </args>
             </payloadFactory>
             <property name="messageType" value="application/xml"/>
             <log level="full"/>
             <send>
                <endpoint>
                   <address uri="jms:/testQueue?transport.jms.ConnectionFactoryJNDIName=QueueConnectionFactory&java.naming.factory.initial=org.wso2.andes.jndi.PropertiesFileInitialContextFactory&java.naming.provider.url=repository/conf/jndi.properties&transport.jms.DestinationType=queue"/>
                </endpoint>
             </send>
          </case>
       </switch>
    </outSequence>
 </target>
 <description/>
</proxy>

在inSequence中，我将客户端的请求转发给Rest服务，Rest服务的响应是一个json字符串，如下所示：

{
  "codice":"0",
  "messaggio":"Operazione effettuata 18:12",
  "path":"\/path\/1AASSCOGNOME_NOME.111.2231\/",
  "documenti":[{
            "idAggregatoContenitore":"3508",
            "idDocumento":"016601",
            "idVersione":"17010",
            "numVersione":"1",
            "tipoDocumento":"Documento",
            "autore":"sysadmin",
            "titolo":"prova1",
            "fileName":"FStandard.xml",
            "checkedOut":"false",
            "idDocumentoPadre":"",
            "flagAllegati":"false",
            "flagDaProtocollare":"true",
            "dataCreazione":"11\/02\/2013 19:05",
            "dataChekin":"11\/02\/2013 19:05",
            "mimeType":"text\/xml",
            "empty":"false",
            "data":"1660100000",
            "cache":"false",
            "tipo":"D",
            "nome":"prova1",
            "keyData":"16601",
            "keyNome":"prova1",
            "keyNumero":"",
            "keyTipo":"D",
            "fileExtension":"path\/xml_file.png",
            "evidenza":"false",
            "originalDocumentoPadreId":"",
            "originalDocumentoId":"016601",
            "originalAggregatoContenitoreId":"3508"
          },
          {
            "idAggregatoContenitore":"3508",
            "idDocumento":"016602",
            "idVersione":"17011",
            "numVersione":"1",
            "tipoDocumento":"Documento",
            "autore":"sysadmin",
            "titolo":"123456789",
            "fileName":"HTTP Proxy Server.jmx",
            "checkedOut":"false",
            "idDocumentoPadre":"",
            "flagAllegati":"false",
            "flagDaProtocollare":"true",
            "dataCreazione":"11\/02\/2013 19:19",
            "dataChekin":"11\/02\/2013 19:19",
            "mimeType":"application\/octet-stream",
            "empty":"false",
            "data":"1660200000",
            "cache":"false",
            "tipo":"D",
            "nome":"123456789",
            "keyData":"16602",
            "keyNome":"123456789",
            "keyNumero":"",
            "keyTipo":"D",
            "fileExtension":"path\/Documento.png",
            "evidenza":"false",
            "originalDocumentoPadreId":"",
            "originalDocumentoId":"016602",
            "originalAggregatoContenitoreId":"3508"
          }],
  "data":"350800000",
  "tipoAggregatoEnum":"R",
  "statoEnum":"aperto",
  "keyData":"1360602720000",
  "keyNome":"1aasscognome_nome.111.2231",
  "nomeAggregatoNoNumero":"1AASSCOGNOME_NOME.111.2231",
  "keyNumero":"1AASSCOGNOME_NOME.111.2231",
  "keyTipo":"R",
  "originalAggregatoId":"3508",
  "originalAggregatoPadre":"3108"
}

作为标准行为，ESB将传入的json消息转换为xml格式的消息 . 现在在outSequence我想：

1）通过调解器将RestService响应发送回客户端

2）然后我想构建一个xml消息，从消息有效负载中提取一些元素，然后通过jms协议在其他地方发送它 .

除了PayloadFactory中介之外，代理工作正常 . 实际上，Payload Factory介体构建的消息的主体是空的：

<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope">
<Body>
  <code xmlns="http://ws.apache.org/ns/synapse"/>
</Body>
</soapenv:Envelope>

谁能告诉我为什么指定的arg标签是空的（xpath表达式似乎是正确的）？怎么了？谢谢