async getCustomer(id, options = {}) {
        debug(`getCustomer(${id}, ${JSON.stringify(options)})`);
        try {
            await this._rateLimitBucket.throttle();
            if (options.expand) {
                options.expand.push('subscriptions');
            } else {
                options.expand = ['subscriptions'];
            }
            const customer = await this._stripe.customers.retrieve(id, options);
            debug(`getCustomer(${id}, ${JSON.stringify(options)}) -> Success`);
            return customer;
        } catch (err) {
            debug(`getCustomer(${id}, ${JSON.stringify(options)}) -> ${err.type}`);
            throw err;
        }
    }
Retrieve the Stripe Customer object by ID.

@param {string} id
@param {ICustomerRetrieveParams} options

@returns {Promise<ICustomer|IDeletedCustomer>}
@throws {Error}