JSON转换为CSV /如何修复_csv.Error：可迭代，而不是NoneType

Question

已经编写了一些代码，以获取包含JSON文件的目录，并创建一个新的CSV文件，以将其所有数据显示在一个位置。我想我快要到了，但是最终会收到此错误：

_csv.Error: iterable expected, not NoneType

所有JSON文件如下所示：

{
  "data": [
    {
      "ticker": "NDX",
      "tradeDate": "2017-01-03",
      "expirDate": "2017-01-06",
      "dte": 4,
      "strike": 3300,
      "stockPrice": 4900.5,
      "callVolume": 0,
      "callOpenInterest": 0,
      "callBidSize": 10,
      "callAskSize": 1,
      "putVolume": 0,
      "putOpenInterest": 0,
      "putBidSize": 0,
      "putAskSize": 2,
      "callBidPrice": 1593.1,
      "callValue": 1600.64,
      "callAskPrice": 1607.5,
      "putBidPrice": 0,
      "putValue": 0,
      "putAskPrice": 2.2,
      "callBidIv": 0,
      "callMidIv": 2.190066,
      "callAskIv": 2.190066,
      "smvVol": 0.160588,
      "putBidIv": 0,
      "putMidIv": 1.866392,
      "putAskIv": 1.866392,
      "residualRate": 0,
      "delta": 1,
      "gamma": -3.01422e-15,
      "theta": -0.0470117,
      "vega": 9.14631e-11,
      "rho": 0.2721,
      "phi": -0.404087,
      "driftlessTheta": -2.29457e-8,
      "extSmvVol": 0.242996,
      "extCallValue": 1600.5,
      "extPutValue": 0,
      "spotPrice": 4900.51,
      "updatedAt": "2019-04-02 10:27:11"
    }
  ]
}

这是代码（我用来定义要处理的字段列表的示例JSON文件仅称为“输出”，位于“选项”上方的文件夹中）。 Output.csv（目标文件）也位于“选项”上方的文件夹中：

def get_list_of_json_files():

    list_of_files = os.listdir('options')

    return list_of_files

def create_list_from_json(out):

    with open(out) as f:

        data = json.load(f)

    data_list = []

    data_list.append(data["data"][0]["ticker"])

    data_list.append(data["data"][0]["other fields"])

def write_csv():

    list_of_files = get_list_of_json_files()

    for file in list_of_files:

        row = create_list_from_json(f'options/{file}')

        with open('output.csv', 'a') as c:

            writer = csv.writer(c)

            writer.writerow(row)

        c.close()

if __name__ == '__main__':

    write_csv()