Join in the Scala streams API is currently unusable in 2.0.0 as reported by @mowczare:
#5019 (comment)
This due to an overload of it with the same signature in the first curried parameter.
See compiler issue that didn't catch it: https://issues.scala-lang.org/browse/SI-2628
Reviewers: Debasish Ghosh <dghosh@acm.org>, Guozhang Wang <guozhang@confluent.io>, John Roesler <john@confluent.io>