How to reproduce these conditions

Sample name or URL where you found the bug
fcm-notification

Failing Function code used (including require/import commands at the top)
Update fcm-notification sample to use latest API instead of legacy API with reference to https://stackoverflow.com/questions/50505274/why-use-a-legacy-api-for-a-firebase-fcm-notifications-sample/50510755#50510755

Steps to set up and reproduce
Line 74 of https://github.com/firebase/functions-samples/blob/master/fcm-notifications/functions/index.js