[READ] Step 1: Are you in the right place?

• For issues or feature requests related to the code in this repository
  file a Github issue.
  • If this is a feature request make sure the issue title starts with "FR:".
• For general technical questions, post a question on StackOverflow
  with the firebase tag.
• For general Firebase discussion, use the firebase-talk
  google group.
• For help troubleshooting your application that does not fall under one
  of the above categories, reach out to the personalized
  Firebase support channel.

[REQUIRED] Step 2: Describe your environment

• Operating System version: Mac OS High Sierra (10.13.1)
• Firebase SDK version: firebase: (^4.5.1)
• Library version: firebase-admin (^5.4.2)
• Firebase Product: FCM / admin.messaging()

[REQUIRED] Step 3: Describe the problem

NodeJS program doesn't terminate after running FCM command.

Steps to reproduce:

• save the following code as: fcm-test.js
• run the code with

node fcm-test.js

• In my enviroment, it'll not stop untill you forcefully stop it by pressing CTRL+C.

Relevant Code:

const admin = require('firebase-admin');
const serviceAccount = require("../../../service-accounts/production.json");
const registrationTokens = require('./tokens');
// ["someShortString1:someLongString1", "someShortString2:someLongString2", ...];
admin.initializeApp({
  credential: admin.credential.cert(serviceAccount)
})
const body = 'body';
const title = 'title';
const payload = {
  data: {
    body,
    title
  },
  notification: {
    body,
    title
  }
}
const fcm = admin.messaging();
const printJSON = (thing) => { console.log(JSON.stringify(thing, null, 2))};
fcm.sendToDevice(registrationTokens, payload).then(printJSON).catch(printJSON);