Github user mjsax commented on the pull request: https://github.com/apache/flink/pull/983#issuecomment-127597013 I double checked with two different programs and it worked... Not sure if I am missing something. Please see dev mailing list. Otherwise, please help me to come up with an example that breaks serialization such that I can use this example to fix the code. I did not try comparators though: not sure for what this would be helpful? There is no data in Tuple0 so there is nothing to compare with. IMHO, all Tuple0 object are equal to each other. I don't see any use case to group on Tuple0, thus, comparators are not required from my point of view and should not be supported.
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