THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Users who want to keep the current behavior can prepend a .filter() operator to the aforementioned operators and filter accordingly.
E.g.
//ifwhen the old behavior is needed
leftStream.filter((key, value) -> key != null)
.leftJoin(rightStream, (lv, rv) -> join(lv, rv), windows);
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