问wso2的属性中介器中的级联操作无效

EN

{
    "userId": 10,
    "code": 1,
    "body": {
        "id": 2,
        "endpoint": "some-key",
        "1": {
            "anotherId": 30,
            "title": "Lorum ipsum",
            "some-key": "some value here"
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?><sequence xmlns="http://ws.apache.org/ns/synapse" name="mediation-sequence">

    <script language="js">
        <![CDATA[

            // read the JSON payload from the message context
            var payload = mc.getPayloadJSON();

            // read the property values
            var code = payload["code"];
            var endpoint = payload["body"]["endpoint"];

            var extracted_value = payload["body"][code][endpoint];

            // set the extracted value as property to message context
            mc.setProperty("ExtractedValue", extracted_value);
        ]]>
    </script>

    <log level="custom">
        <property name="Extracted value" expression="$ctx:ExtractedValue" />
    </log>
</sequence>