node.jsを使ってgoogle spreadsheetの値をとる部分でのエラー

Question

前提・実現したいこと

node.jsを使ってgoogle spreadsheetの値をとり、それを加工する
シートの読み取り部分クラス化 加工部分はメイン

発生している問題・エラーメッセージ

何が問題かわからない

(node:26599) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'context' of undefined
    at get (/home/pi/git/node_modules/googleapis/build/src/apis/sheets/v4.js:570:31)
    at Promise (internal/util.js:275:30)
    at new Promise (<anonymous>)
    at get (internal/util.js:274:12)
    at googleSheet.read (/home/pi/git/googleSheet.js:41:22)
(node:26599) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:26599) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

該当のソースコード

const fs = require('fs');
const { promisify } = require('util');
const { google } = require('googleapis');
const { OAuth2Client } = require('google-auth-library');
const sheets = google.sheets('v4');

const readFileAsync = promisify(fs.readFile);
const ssValuesGetAsync = promisify(sheets.spreadsheets.values.get);


module.exports = class googleSheet {
    constructor() {
        this.TOKEN_DIR = __dirname + "/token";
        this.TOKEN_PATH = this.TOKEN_DIR + '/sheets.googleapis.com-nodejs-quickstart.json';
        this.sheet_id = "*******************************************";
    }

    async read() {
        const content = await readFileAsync(__dirname + '/token/client_secret.json');
        const credentials = JSON.parse(content);

        const clientSecret = credentials.installed.client_secret;
        const clientId = credentials.installed.client_id;
        const redirectUrl = credentials.installed.redirect_uris[0];
        const oauth2Client = new google.auth.OAuth2(clientId, clientSecret, redirectUrl);
        const token = await readFileAsync(this.TOKEN_PATH);
        oauth2Client.credentials = JSON.parse(token);

        const apiOptions = {
            auth: oauth2Client,
            spreadsheetId: this.sheet_id,
            range: 'A1:D36',
        };

        return await ssValuesGetAsync(apiOptions, { context: google.auth });
    }
}

###受け取り側

const googleSheet = require('./googleSheet');
const gsheet = new googleSheet(); 

...

let sheet = await gsheet.read();

試したこと

プロミス化している部分でのエラーというところまでは調べました。

補足情報（FW/ツールのバージョンなど）

raspberrypi3ｂ+
Linux raspberrypi 4.14.98-v7+ #1200 SMP Tue Feb 12 20:27:48 GMT 2019 armv7l GNU/Linux
node v10.15.3
"@google-cloud/translate": "^3.0.1",
"dotenv": "^8.0.0",
"google-auth-library": "^3.1.2",
"googleapis": "^39.2.0",
"tmi.js": "^1.4.2",
"util": "^0.12.0"

Answer 1

const ssValuesGetAsync = promisify(sheets.spreadsheets.values.get);

↓

const ssValuesGetAsync = promisify(sheets.spreadsheets.values.get.bind(sheets))