Invalid typings of the first parameter of `firestore.onChange` - optional before, after

[merlinnot]

Related issues

None found.

[REQUIRED] Version info

node: v10.15.1

firebase-functions: v2.2.0

firebase-tools: v6.3.1

firebase-admin: ^7.0.0

[REQUIRED] Test case

import { firestore } from 'firebase-functions';

firestore
  .document('collection/{documentId}')
  .onUpdate(change => change.after.data());

[REQUIRED] Steps to reproduce

Try to compile the above snippet using the latest version of TypeScript compiler (v3.3.0 at the time) with strictNullChecks enabled.

Compilation will fail with the following error:

test.ts:5:23 - error TS2532: Object is possibly 'undefined'.

5   .onUpdate(change => change.after.data());
                        ~~~~~~~~~~~~


Found 1 error.

[REQUIRED] Expected behavior

Typings should not define before nor after as optional, according to the docs:

function(non-null functions.Change containing non-null functions.firestore.DocumentSnapshot, optional non-null functions.EventContext)
Event handler which is run every time data is updated in Cloud Firestore.
Value must not be null.

[REQUIRED] Actual behavior

See Steps to reproduce.

Were you able to successfully deploy your functions?

Not applicable.