takeLast emits undefined it applied with no params

[kievsash]

Bug Report

Current Behavior
takeLast() operator when applied without any param returns undefined.

Reproduction
https://codepen.io/kievsash/pen/dEgyGX?editors=0010

let Rx = window.Rx = window['rxjs'];
let {forkJoin, Subject, merge, of} = Rx;
let {ajax} = Rx.ajax;
let {map, finalize, tap, takeLast, scan} = Rx.operators;
console.clear();


const m$ = ajax('https://jsonplaceholder.typicode.com/comments/1').pipe(takeLast()); // incorrect

//const m$ = ajax('https://jsonplaceholder.typicode.com/comments/1').pipe(takeLast(1)); // correct

m$.subscribe(console.warn)

Expected behavior
WEll, should be discussed I guess. I propose that takeLast() to work like takeLast(1) -

Environment

• Runtime: Chrome Version 74.0.3729.169 (Official Build) (64-bit)
• RxJS version: https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.5.2/rxjs.umd.min.js

Possible Solution
To set count=1 by default here: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/takeLast.ts#L50

Additional context/Screenshots

[kwonoj]

Since our interface strictly requires param, it's more like an edge case. If I were to amend behavior, I'd rather throw argumentRangeError as same as non-acceptable count param instead of implicitly fallback to other behavior.

[kievsash]

Ok, If it is final decision I can try to provide pull request with expected behavior.

[kievsash]

@cartant Kindly take a look: #4854

[kwonoj]

#5326