When calling KTable.groupBy on the result of a KTable-KTable join, NPEs are raised:
The root cause is that the join is expected to emit null values when no match is found, but KTableRepartitionMap is not set up to handle this case.
On the users email list, Guozhang Wang described a plan of action:
I think this is actually a bug in KTableRepartitionMap
that it actually should expect null grouped keys; this would be a
straight-forward fix for this operator, but I can make a pass over all the
repartition operators just to make sure they are all gracefully handling