How to generate a JSON string contains Array?

[Anonymous]

On TOS 6.1, I am trying to generate a JSON string contains one Array element. There is a ArrayList type "imageIds" in input schema of tWriteJSONField, and bind to "element" field which is an loop element in output schema.
However, as in output, I found there's additional "[]":
{
    "accountid": "1",
    "token": "rAXRRuapwDsO5A",
    "initialContent": {
        "wxUserId": "o9-uWuNuTZgTW2p_FYzzZ5E2dGuA",
        "productType": "1",
        "description": "?????\n??",
        "serverPhotoIds": [     <-----unexpected
            [
                "60e5a503-0c23-11e6-a5c9-d1b1a1c2ca83",
                "610fc244-0c23-11e6-a5c9-43ab28439981",
                "61334fd5-0c23-11e6-a5c9-c3176c103283"
            ]
        ]                              <-----unexpected
    }
}

[Anonymous]

Hi
Don't need to set an attribute @class to serverPhotoIds element. 


Regards
Shong