Github user fhueske commented on the issue:
https://github.com/apache/flink/pull/5016
Hi @xccui, thanks for the update. Regarding your questions:
1. I think `null` should not be supported.
2. Such a `TimestampExtractor` is already available:
[`StreamRecordTimestamp`](https://github.com/apache/flink/blob/master/flink-libraries/flink-table/src/main/scala/org/apache/flink/table/sources/tsextractors/StreamRecordTimestamp.scala)
:-)---
