[GitHub] [kafka] rhauch commented on pull request #9306: KAFKA-10477: Enabling the same behavior of NULL JsonNodeType to MISSI…

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rhauch commented on pull request #9306:
URL: https://github.com/apache/kafka/pull/9306#issuecomment-702443976


   Thanks for putting together this comprehensive list of AK versions, Jackson versions, and behavior.
   
   > * ak v2.3.0 -> j v2.9.9 [Looks like an outlier, where ak version increased with a decrease in jackson-databind version]
   I don't think this was an outlier. If you sort them by release dates, things look a bit more logical and you can see how the Jackson versions only continually increase over time:
   
   ak v2.1.0 (2018-11-20)-> j v2.9.7
   ak v2.1.1 (2019-02-15) -> j v2.9.8
   ak v2.2.0 (2019-03-22) -> j v2.9.8
   ak v2.2.1 (2019-06-01) -> j v2.9.8
   ak v2.3.0 (2019-06-24) -> j v2.9.9
   ak v2.3.1 (2019-10-24) -> j v2.10.0
   ak v2.2.2 (2019-12-01) -> j v2.10.0
   ak v2.4.0 (2019-12-13) -> j v2.10.0
   ak v2.4.1 (2020-03-10)-> j v2.10.0
   ak v2.5.0 (2020-04-14) -> j v2.10.2
   ak v2.6.0 (2020-08-03) -> j v2.10.2
   ak v2.5.1 (2020-08-10) -> j v2.10.2
   
   IOW, the following **versions** are all affected since they use Jackson 2.10.x:
   * 2.3.1
   * 2.2.2
   * 2.4.0
   * 2.4.1
   * 2.5.0
   * 2.5.1
   * 2.6.0
   
   and thus the following **branches** are affected since they now use Jackson 2.10.x:
   * `2.2`
   * `2.3`
   * `2.4`
   * `2.5`
   * `2.6`
   
   I've also gone through a number of versions of the https://github.com/FasterXML/jackson-databind code, looking for how MissingNode is used. It's obvious that MissingNode is used a lot more prevalently in 2.10.0. But the documentation for `MissingNode` is as follows:
   
   >  In most respects this placeholder node will act as {@link NullNode};
   > for example, for purposes of value conversions, value is considered
   > to be null and represented as value zero when used for numeric
   > conversions.
   
   So I think it's pretty clear that we should treat `JsonNodeType.MISSING` as null. This is what this PR tries to do, and I'm now less concerned about unexpected behavioral changes after having read and verified this analysis.
   
   Once this PR is merged to `trunk`, this fix will need to be backported to the following **branches** that are all affected because they use Jackson 2.10.x:
   * `2.2`
   * `2.3`
   * `2.4`
   * `2.5`
   * `2.6`


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