Javascript 在vscode中调试时发生firebase管理（节点）异常

使用firebase admin 5.0.0，当我在运行node 7.10.0的vscode 1.12.2中调试时，会出现此异常

Exception has occurred: Error
SyntaxError: Unexpected token ɭ in JSON at position 0
    at Object.parse (native)
    at eb (c:\Users\...\node_modules\firebase-admin\lib\database\database.js:57:267)
    at wc (c:\Users\...\node_modules\firebase-admin\lib\database\database.js:77:489)
    at yc (c:\Users\...\node_modules\firebase-admin\lib\database\database.js:77:708)
    at kh.h.hf (c:\Users\...\node_modules\firebase-admin\lib\database\database.js:224:146)
    at c:\Users\...\node_modules\firebase-admin\lib\database\database.js:239:186
    at c:\Users\...\node_modules\firebase-admin\lib\firebase-app.js:82:25
    at Array.forEach (native)
    at c:\Users\...\node_modules\firebase-admin\lib\firebase-app.js:81:43
    at process._tickCallback (internal/process/next_tick.js:109:7)

这是我正在运行的javascript

'use strict';

if (!process.env.FIREBASE_PROJECT_ID) {
  require('dotenv').config({ silent: true });
}

const fbConfig = require('./firebase-config');
const admin = require('firebase-admin');

admin.initializeApp({
  credential: admin.credential.cert(fbConfig.FIREBASE_SERVICE_ACCOUNT),
  databaseURL: fbConfig.APP_SETTINGS.databaseURL
});

const db = admin.database();

let obj = {foo:'bar'};

let ref = db.ref('test');

ref.set(obj, function (error) {
  console.log(error);
  console.log('complete');
});

异常发生在database.js中

function eb(a) { 
  return "undefined" !== typeof JSON && n(JSON.parse) ? JSON.parse(a) : xa(a) 
}

当我点击异常时，我可以看到

a

的值是“ɭ”�". 如果我继续，将引发另一个类似的异常，操作最终成功完成，错误值为null

知道这是怎么回事吗