Firestore 0.15.2 regression: AssertionError [ERR_ASSERTION]: missing path

[hiranya911]

Following regression was observed in the last Firestore release. Happened on both Mac and Linux environments (Node 6 and 8 respectively)

$ cat index.js
const Firestore = require('@google-cloud/firestore');
console.log('success');

$ npm install @google-cloud/firestore@0.15.2
$ node index.js 
assert.js:42
  throw new errors.AssertionError({
  ^

AssertionError [ERR_ASSERTION]: missing path
    at Module.require (module.js:594:3)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/hkj/Projects/firebase-admin-node/temp/node_modules/@google-cloud/firestore/build/src/index.js:24:20)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)

$ rm -r node_modules
$ npm install @google-cloud/firestore@0.14.0
$ node index.js 
success