Standardize <void>ReplaySubject to behave like <void>Subject

[euangoddard]

RxJS version: 5.5.6

Code to reproduce:

const replaySubject = new ReplaySubject<void>(1);
// At some later point
replaySubject.next();

Expected behavior: I can call next() without any arguments since the subject is a void type.

Actual behavior: I have to call next() with undefined or null to signal that something has happened to the replay subject.

Additional information: Essentially I want to use a replay subject to indicate whether something has happened. I need to use a ReplaySubject so that new subscribers connecting can know whether the subject has emitted in the past, but the value that subject emits is irrelevant to any subscribers (hence using a void replay subject).

This behaviour seems at odds with how Subject works and their implementation of next() differs. I noticed that this behaviour was changed here: #1728, but am unsure whether my proposed change will be accepted given this issue: #2852

I will be happy to submit a PR for this if this change would be accepted.

[kwonoj]

As discussed in #3074, we will wait for upstream change microsoft/TypeScript#12400 (comment) to properly support behavior around those. We probably won't going to introduce interim changes until then as it may break between changes we introduce.

[BioPhoton]

@kwonoj or @cartant

This is already resolved. I tested it.

So imho this issue can be closed.

[cartant]

Closing this because the problem has been resolved in v7 - in #5307, IIRC.