使用DataWave2.0 mule4在XML数组中添加递增的数字？

<mule xmlns:xml="http://www.mulesoft.org/schema/mule/xml" xmlns:dataweave="http://www.mulesoft.org/schema/mule/dataweave" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
    xmlns:spring="http://www.springframework.org/schema/beans" version="EE-4.3.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
    http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
    http://www.mulesoft.org/schema/mule/xml http://www.mulesoft.org/schema/mule/xml/current/mule-xml.xsd
    http://www.mulesoft.org/schema/mule/dataweave http://www.mulesoft.org/schema/mule/dataweave/current/mule-dataweave.xsd">

    <xml:xml-to-dw-transformer name="XML_to_DW" doc:name="XML to DW">
        <xml:input-xml-transformer />
        <dataweave:dw-template><![CDATA[%dw 2.0
output application/xml
---
payload map ((item, index) -> item ++ {id: index + 1})]]></dataweave:dw-template>
    </xml:xml-to-dw-transformer>

    <flow name="add-incremental-number">
        <http:listener doc:name="Listener" config-ref="HTTP_Listener_config" path="/add-incremental-number" allowedMethods="POST" />
        <set-payload value="#[payload]" doc:name="Set Payload" />
        <xml:xml-to-dw-transformer doc:name="XML to DW" />
        <flow-ref name="add-incremental-number-subflow" doc:name="add-incremental-number-subflow" />
        <xml:dw-to-xml-transformer doc:name="DW to XML" />
        <set-payload value="#[payload]" doc:name="Set Payload" />
    </flow>

    <sub-flow name="add-incremental-number-subflow">
        <foreach doc:name="For Each" collection="#[payload]">
            <set-payload value="#[payload]" doc:name="Set Payload" />
            <set-variable variableName="index" value="#[flowVars['foreach-index'] + 1]" doc:name="Variable" />
            <dataweave:transform doc:name="Transform Message">
                <dataweave:output-encoding>UTF-8</dataweave:output-encoding>
                <dataweave:input-encoding>UTF-8</dataweave:input-encoding>
                <dataweave:input-dw><![CDATA[%dw 2.0
output application/xml
---
payload ++ {number: vars.index}]]></dataweave:input-dw>
            </dataweave:transform>
            <set-payload value="#[payload]" doc:name="Set Payload" />
        </foreach>
    </sub-flow>
</mule>