Fix RxSession.beginTransaction returning an empty Publisher

[injectives]

This update is to fix: #797

[michael-simons]

The changes make sense in an isolated view, and I approve them.

But: Shouldn't than the examples in #797 fail with "Unexpected condition, begin transaction call has completed successfully with transaction being null"?

Anyway, please back port to 4.2 and 4.1 as well… Might even go down to 4.0. @gjmwoods and I would like to release patches of those versions as well for the time being.

[injectives]

The changes make sense in an isolated view, and I approve them.

Thank you. 👍

But: Shouldn't than the examples in #797 fail with "Unexpected condition, begin transaction call has completed successfully with transaction being null"?

Based on the reproduction, null value was not actually the problem. The transaction is actually checked for null value in both cases (here and here). The actual change is around how MonoSink is used. It used to be completed twice, one time with value and one without.

Anyway, please back port to 4.2 and 4.1 as well… Might even go down to 4.0. @gjmwoods and I would like to release patches of those versions as well for the time being.

Sure.