Github user sihuazhou commented on the issue:
https://github.com/apache/flink/pull/5993
I made an additional fixup to `StateBackendTestBase#testMapState()` to
guard this fix in the future, @kl0u please free feel to let me know if you want
to revert it. I do this because this bug wasn't be discovered by the current
tests. The reason is that the tests related to the `getSerializedValue()` (e.g
`StateBackendTestBase#testMapState()`) used the `Integer` as the backend key
type, which will has the same `userKeyOffset` for every entry, I change it to
`String` so that it can trigger the exception for the old code and guard this
fix in the future.
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