[GitHub] satybald commented on issue #6724: [FLINK-10380] Add precondition for assignToKeyGroup method

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satybald commented on issue #6724: [FLINK-10380] Add precondition for assignToKeyGroup method
URL: https://github.com/apache/flink/pull/6724#issuecomment-427952541
 
 
   @StephanEwen thank you for feedback! From what I see, `KeyGroupRangeAssignment#assignToKeyGroup` is utility class. It has 36 usages in different classes: state backends, operators, and tests. `AbstractKeyedStateBackend#setCurrentKey`, which uses the utilty method has 296 usages.
   
   I'm bit afraid that catching and testing NPE earlier in the chain requires a significant effort to rewrite everything without much benefit. As try/catch doesn't make code cleaner and adding the same error message will violate DRY principle. 
   
   Also, determine if the key is null earlier in the chain without preconditions with try/catch might lead to false positives as there's another reason for child method throwing NPE.
   
   From what I see `computeKeyGroupForKeyHash(key.hashCode(), maxParallelism);` is the place where key group index calcluated and NPE is thrown in case key is null. Would you agree that catching NPE in utility class and overriding with a specific message is viable alternative?

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