如何在Mulesoft 4中POST请求中存在id字段时抛出错误消息

<flow name="postFlow">
    <http:listener path="/api/resource" allowedMethods="POST" config-ref="HTTP_Listener_Configuration" />
    <set-payload value="#[payload as Object]" />
    <choice>
        <when expression="#[payload.id != null]">
            <set-variable variableName="errorMessage" value="ID field is not allowed in the request" />
            <throw-exception exceptionClass="org.mule.runtime.core.api.exception.MessagingException" doc:name="Throw Exception">
                <message>
                    <error-response>
                        <set-payload value="#[{'error': flowVars.errorMessage}]" />
                        <set-property propertyName="http.status" value="400" />
                        <set-property propertyName="Content-Type" value="application/json" />
                    </error-response>
                </message>
            </throw-exception>
        </when>
        <otherwise>
            <!-- Continue with normal processing -->
        </otherwise>
    </choice>
</flow>