Github user StephanEwen commented on the issue:
https://github.com/apache/flink/pull/4877
Thanks for opening this pull request.
I think it is correct that `SourceFunction` is not required to implement
`Serializable`. But I think it does not cause any problems, as far as I know,
it has no implication at all on the runtime or behavior.
It does serve as a "reminder" that sources need to be serializable, so it
could actually be helpful to keep it.
Given that it makes no difference, should we keep it?
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