[REQUIRED] Environment info

firebase-tools: 6.8.0

Platform: Windows 10

[REQUIRED] Test case

I had a set of functions built using Node.js version 6. They were successfully deployed and running.

I took the following actions to upgrade to use a newer version of Node:
-- Upgraded my Windows development system to Node.js version 10.15.3
-- Upgraded to latest Firebase tools: npm install -g firebase-tools
-- Upgraded Firebase SDK: npm install firebase-functions@latest firebase-admin@latest --save
-- Edited the project's package.json file to include "engines" : { "node" : "10" }

With those changes, the firebase deploy --only functions command completed without error. However, immediately after deployment, an error log appeared in the Firebase console for each function: Warning, FIREBASE_CONFIG environment variable is missing. Initializing firebase-admin will fail.

Changing package.json file to specify version 8 instead of 10 resolved the problem: "engines" : { "node" : "8" } . Functions initialize and execute as expected.

[REQUIRED] Steps to reproduce

Described in test case

[REQUIRED] Expected behavior

Firebase tools should set FIREBASE_CONFIG to the appropriate default for the project.

[REQUIRED] Actual behavior

FIREBASE_CONFIG is not set if Node version of 10 is specified in package.json file.