:vendor:calcite-1_20_0:validateVendoring fails

This error was reported on Slack: https://the-asf.slack.com/archives/C9H0YNP3P/p1586911958184200

"I encountered this error when I built Beam from master branch. Is it a known issue? It happens in beam 2.21 and master branch, but the build works fine in 2.20."

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• What went wrong:
  Execution failed for task ':vendor:calcite-1_20_0:validateVendoring'.
  > /home/yangzhan/oss/beam/vendor/calcite-1_20_0/build/libs/beam-vendor-calcite-1_20_0-0.2.jar exposed classes outside of org.apache.beam namespace: [/home/yangzhan/oss/beam/vendor/calcite-1_20_0/build/tmp/expandedArchives/beam-vendor-calcite-1_20_0-0.2.jar_ee40b0aab4e7709d8d80d205ee8852ba/module-info.class]
• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
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