[Bug]: Portable translation or SDK harness appears to have a bug in GBK coders

[kennknowles]

What happened?

In the implementation of Redistribute as a simple composite with no special handling, the portable Java-based runners as well as the ULR have a common failure:

Error received from SDK harness for instruction 3: org.apache.beam.sdk.util.UserCodeException: java.lang.ClassCastException: org.apache.beam.sdk.util.WindowedValue$ValueInGlobalWindow cannot be cast to java.lang.String

See e.g.

Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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