StreamsBuilder.build fails with StreamsException "Found a null keyChangingChild node for OptimizableRepartitionNode"

We created a topology using Streams DSL (topology description is available in the attached topology-description.txt, no optimization).

Topology works fine with topology.optimization=none, however it fails to build with StreamsException "Found a null keyChangingChild node for OptimizableRepartitionNode" if we set topology.optimization=all (exception stack trace is attached streams-exception-log.txt).

We used https://zz85.github.io/kafka-streams-viz/ to visualize topology and try to guess what might be upsetting optimizer, yet did not manage to figure it out ourselves.