有关使用axios修改响应主体对象的问题

Question

抱歉，如果格式不正确。我目前正在使用Express路由器使用axios向第三方api发出请求。我正在尝试使用transformResponse修改响应对象，以便更好地使用结果。问题是当这样调用时，节点会以“ typeError：无法将未定义或null转换为对象”作为响应

router.use(bodyParser.urlencoded({ extended: true }));
router.use(bodyParser.json());

router.get('/', (req, res) => {
axios.get(`${stockURL}?symbol=googl`, {
    params: {
        function: 'TIME_SERIES_DAILY',
        apikey: ALPHA_KEY,
        outputsize: 'full'
    },
    transformResponse: [function (data) {
        // Do whatever you want to transform the data
        function fixKeys(obj) {
            Object.keys(obj).forEach(function (key) {
                let newKey = key.split('.')[1].trim();
                //dynamic form of obj.newKey
                obj[newKey] = obj[key];
                delete obj[key];
            });
            return obj;
        }
        //the main object with all dates by day
        // let fullData = data[stockDay.json];
        let fullData = data['Time Series (Daily)'];

        let arrayData = [];
        // adds a key value pair for the date, with the date of the stock quote, 
        //and then deletes the key 'Time Series (Daily)'
        Object.keys(fullData).map(function (key) {
            let obj = {};
            obj = fixKeys(fullData[key]);
            obj['date'] = key;
            arrayData.push(obj);
        });
        //current days data
        todayData = arrayData[0];
        //get 52 week high/low
        let arrayLow = [];
        let arrayHigh = [];
        for (let i = 0; i < 365 && i < arrayData.length; i++) {
            arrayLow.push(parseInt(arrayData[i].low));
            arrayHigh.push(parseInt(arrayData[i].high));
        }
        todayData['tlow'] = Math.min.apply(null, arrayLow);
        todayData['thigh'] = Math.max.apply(null, arrayLow);
        return todayData;
    }]
})
    .then((payload) => {
        console.log(payload.todayData)
        res.json(payload.todayData);
    })
    .catch((err) => {
        console.error(err);
        res.status(500).json({
            message: 'Something went wrong while querying Alphavantage'
        })
    })
});