issues deleting an image using firebase functions and @google-cloud/storage

I'm trying to create a script in firebase functions that will react to a db event and remove an image that has its path in one of the params ("fullPath").

this is the code i'm using:

'use strict';

const functions = require('firebase-functions');
const request = require('request-promise');
const admin = require('firebase-admin');
const gcs = require('@google-cloud/storage')({
    projectId: 'XXXXXXX',
    credentials: {
        // removed actual credentials from here
    }});

admin.initializeApp(functions.config().firebase);

// Deletes the user data in the Realtime Datastore when the accounts are deleted.
exports.removeImageOnNodeRemoval = functions.database
    .ref("images/{imageId}")
    .onWrite(function (event) {

        // exit if we are creating a new record (when no previous data exists)
        if (!event.data.previous.exists()) {
            console.log("a new image added");
            return;
        }

        // exit if we are just trying to update the image
        if (event.data.exists()) {
            console.log("image is been modified");
            return;
        }

        let previousData = event.data.previous.val();
        if(!previousData || !previousData.fullPath){
            console.log("no data in the previous");
            return;
        }

        let bucketName = 'XXXXXXX';
        console.log("default bucketName", gcs.bucket(bucketName));
        let file = gcs.bucket(bucketName).file(previousData.fullPath);
        console.log('the file /'+previousData.fullPath, file);

        file.exists().then(function(data) {
            let exists = data[0];
            console.info("file exists", exists);
        });

        file.delete().then(function() {
            // File deleted successfully
            console.log("image removed from project", previousData.fullPath);

        }).catch(function(error) {
            // Uh-oh, an error occurred!
            console.error("failed removing image from project", error, previousData);
        });

    });

the error i'm getting:

failed removing image from project { ApiError: Not Found
    at Object.parseHttpRespBody (/user_code/node_modules/@google-cloud/storage/node_modules/@google-cloud/common/src/util.js:192:30)
    at Object.handleResp (/user_code/node_modules/@google-cloud/storage/node_modules/@google-cloud/common/src/util.js:132:18)
    at /user_code/node_modules/@google-cloud/storage/node_modules/@google-cloud/common/src/util.js:465:12
    at Request.onResponse [as _callback] (/user_code/node_modules/@google-cloud/storage/node_modules/retry-request/index.js:120:7)
    at Request.self.callback (/user_code/node_modules/@google-cloud/storage/node_modules/request/request.js:188:22)
    at emitTwo (events.js:106:13)
    at Request.emit (events.js:191:7)
    at Request.<anonymous> (/user_code/node_modules/@google-cloud/storage/node_modules/request/request.js:1171:10)
    at emitOne (events.js:96:13)
    at Request.emit (events.js:188:7)
    at IncomingMessage.<anonymous> (/user_code/node_modules/@google-cloud/storage/node_modules/request/request.js:1091:12)
    at IncomingMessage.g (events.js:291:16)
    at emitNone (events.js:91:20)
    at IncomingMessage.emit (events.js:185:7)
    at endReadableNT (_stream_readable.js:974:12)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickDomainCallback (internal/process/next_tick.js:122:9)
  code: 404,
  errors: [ { domain: 'global', reason: 'notFound', message: 'Not Found' } ],
  response: undefined,
  message: 'Not Found' } { contentType: 'image/png',
  fullPath: 'images/1491162408464hznsjdt6oaqtqmukrzfr.png',
  name: '1491162408464hznsjdt6oaqtqmukrzfr.png',
  size: '44.0 KB',
  timeCreated: '2017-04-02T19:46:48.855Z',
  updated: '2017-04-02T19:46:48.855Z' }

i have tried with and without credentials to google-cloud/storage (thinking they might get auto filled while im in firebase.functions - do i need them?). i have tried adding a slash to the file's path. i have validated that the file actually exists in the bucket (even tho file.exists() returns false). the credentials i provided are for an iam i created with admin privileges for the storage service.

i have also enable the billing account on the free plan.

any ideas?

via Ben Yitzhaki