REST API to SOAP proxy cause NULLPAYLOAD error - web-services

Question

I am following REST API to SOAP proxy example, i have changed which WS should to connect and Json structure, when i run the project i got an error of NULLPAYLOAD. when testing using APIKIT
below is my configuration and after it error.
Thanks for the help
<http:listener-config name="api-httpListenerConfig" host="localhost" port="8888" doc:name="HTTP Listener Configuration"/>
<api-platform-gw:api id="rest-api-howto-api" apiName="rest-api-howto-api" version="1.0.0" flowRef="api-main" create="true" doc:name="API Autodiscovery">
</api-platform-gw:api>
<apikit:config name="api-config" raml="api.raml" consoleEnabled="true" consolePath="console" doc:name="Router"/>
<ws:consumer-config name="Web_Service_Consumer" wsdlLocation="http://localhost:9000/SoapContext/SoapPort?wsdl" service="WSStudentRoasterWebService" port="WSStudentRoasterPort" serviceAddress="http://localhost:9000/SoapContext/SoapPort" doc:name="Web Service Consumer"/>
<flow name="api-main">
<http:listener config-ref="api-httpListenerConfig" path="/api/*" doc:name="HTTP"/>
<echo-component doc:name="Echo"/>
<apikit:router config-ref="api-config" doc:name="APIkit Router"/>
<exception-strategy ref="api-apiKitGlobalExceptionMapping" doc:name="Reference Exception Strategy"/>
</flow>
<flow name="get:/loan:api-config">
<dw:transform-message doc:name="Transform to SOAP Request" metadata:id="8c106b2f-1c34-43a4-bac8-d1627b7b6f42">
<dw:input-payload mimeType="application/json" doc:sample="sample_data/json.json"/>
<dw:set-payload><![CDATA[%dw 1.0
%output application/xml
%namespace ns0 http://xxx.edu
---
{
ns0#NewStudentData: {
RoasterSend: {
messageID: payload.loan.MSG
}
}
}]]></dw:set-payload>
</dw:transform-message>
<ws:consumer config-ref="Web_Service_Consumer" operation="NewStudentData" doc:name="SOAP WebService"/>
<dw:transform-message doc:name="Transform from SOAP Response">
<dw:set-payload><![CDATA[%dw 1.0
%output application/json
%namespace ns0 http://www.mulesoft.com/schemas/Mule/Schema.xsd
%namespace ns01 http://xxx.edu
---
{
loan: {
MSG: payload.ns01#NewStudentDataResponse.StudentRoaster_result.messageID
}
}]]></dw:set-payload>
</dw:transform-message>
</flow>
<apikit:mapping-exception-strategy name="api-apiKitGlobalExceptionMapping">
<apikit:mapping statusCode="404">
<apikit:exception value="org.mule.module.apikit.exception.NotFoundException" />
<set-property propertyName="Content-Type" value="application/json" doc:name="Property"/>
<set-payload value="{ "message": "Resource not found" }" doc:name="Set Payload"/>
</apikit:mapping>
<apikit:mapping statusCode="405">
<apikit:exception value="org.mule.module.apikit.exception.MethodNotAllowedException" />
<set-property propertyName="Content-Type" value="application/json" doc:name="Property"/>
<set-payload value="{ "message": "Method not allowed" }" doc:name="Set Payload"/>
</apikit:mapping>
<apikit:mapping statusCode="415">
<apikit:exception value="org.mule.module.apikit.exception.UnsupportedMediaTypeException" />
<set-property propertyName="Content-Type" value="application/json" doc:name="Property"/>
<set-payload value="{ "message": "Unsupported media type" }" doc:name="Set Payload"/>
</apikit:mapping>
<apikit:mapping statusCode="406">
<apikit:exception value="org.mule.module.apikit.exception.NotAcceptableException" />
<set-property propertyName="Content-Type" value="application/json" doc:name="Property"/>
<set-payload value="{ "message": "Not acceptable" }" doc:name="Set Payload"/>
</apikit:mapping>
<apikit:mapping statusCode="400">
<apikit:exception value="org.mule.module.apikit.exception.BadRequestException" />
<set-property propertyName="Content-Type" value="application/json" doc:name="Property"/>
<set-payload value="{ "message": "Bad request" }" doc:name="Set Payload"/>
</apikit:mapping>
</apikit:mapping-exception-strategy>
the error i am getting is below
INFO 2016-12-01 10:21:53,203 [[rest-api-howto_1.0.0].api-httpListenerConfig.worker.01] org.mule.component.simple.LogComponent:
********************************************************************************
* Message received in service: api-main. Content is: ‘{NullPayload}’ *
********************************************************************************
ERROR 2016-12-01 10:21:53,212 [[rest-api-howto_1.0.0].api-httpListenerConfig.worker.01] org.mule.exception.DefaultMessagingExceptionStrategy:
********************************************************************************
Message : Exception while executing:
{NullPayload}
^
Unexpected character ‘N’ at payload#[1:2] (line:column), expected ‘”‘.
Payload : {NullPayload}
Element XML :
%dw 1.0%output application/xml%namespace ns0 http://xxx.edu—{ns0#NewStudentData: {RoasterSend: {messageID: payload.loan.MSG}}}
Payload Type : org.mule.transport.NullPayload
Element : /get:\/loan:api-config/processors/0 # rest-api-howto_1.0.0:rest-api-soap.xml:23 (Transform to SOAP Request)
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