https://beam.apache.org/releases/javadoc/current/org/apache/beam/runners/flink/translation/wrappers/streaming/KvToFlinkKeyKeySelector.html
KvToFlinkKeyKeySelector (Apache Beam 2.73.0)
declaration: package: org.apache.beam.runners.flink.translation.wrappers.streaming, class: KvToFlinkKeyKeySelector
apache beam