Github user greghogan commented on the issue: https://github.com/apache/flink/pull/4525 Hi @XuPingyong thanks for submitting this PR. I'm not clear on why the `null` check was added in FLINK-4075 and `ContinuousFileProcessingTest` is not running locally for me. When calling `InputFormat#nextRecord` we can only reuse the returned object. The object passed to `nextRecord` may be reused internally by the `InputFormat` so we cannot simply pass in the same object. It would be better to move `OUT nextElement = serializer.createInstance();` into the outer loop.
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