"2. Documents in AngularFirestore" needs an `undefined`

[tdkehoe]

In

https://github.com/angular/angularfire/blob/master/docs/firestore/documents.md

line 17 is:

item: Observable<Item>;

should be

item: Observable<Item | undefined>;

Everything else works perfectly. Thanks!

Version info

Angular:

Firebase:

AngularFire:

Other (e.g. Ionic/Cordova, Node, browser, operating system):

How to reproduce these conditions

Failing test unit, Stackblitz demonstrating the problem

Steps to set up and reproduce

Sample data and security rules

Debug output

** Errors in the JavaScript console **

** Output from firebase.database().enableLogging(true); **

** Screenshots **

Expected behavior

Actual behavior