Robin Trietsch created BEAM-4114:
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Summary: Allow null as leftNullValue/rightNullValue in
Join.fullOuterJoin()
Key: BEAM-4114
URL: https://issues.apache.org/jira/browse/BEAM-4114
Project: Beam
Issue Type: Improvement
Components: sdk-java-core
Affects Versions: 2.4.0
Reporter: Robin Trietsch
Assignee: Kenneth Knowles
When using the
[Join.fullOuterJoin()|https://beam.apache.org/documentation/sdks/javadoc/2.4.0/org/apache/beam/sdk/extensions/joinlibrary/Join.html#fullOuterJoin-org.apache.beam.sdk.values.PCollection-org.apache.beam.sdk.values.PCollection-V1-V2-],
a checkNotNull() is done for the
[leftNullValue|https://github.com/apache/beam/blob/master/sdks/java/extensions/join-library/src/main/java/org/apache/beam/sdk/extensions/joinlibrary/Join.java#L207]
and
[rightNullValue|https://github.com/apache/beam/blob/master/sdks/java/extensions/join-library/src/main/java/org/apache/beam/sdk/extensions/joinlibrary/Join.java#L208].
However, it makes more sense to allow null values, since sometimes, if the key
used for the join is not the same, you'd like to see that the value will become
null. This should be decided by the developer, and not by the join library.
Looking at the source code, this is also supported by
[KV.of()|https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/values/KV.java#L42]
(it allows null values), which is used in Join.fullOuterJoin().
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