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https://issues.apache.org/jira/browse/KAFKA-16858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17850174#comment-17850174
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Greg Harris commented on KAFKA-16858:
-------------------------------------
It looks like this should probably be a DataException. We use arrayOfNull() in
Values/SimpleHeaderConverter when inferring the schema for an empty array, and
generally assume that when a root value is schema'd, that all contained values
(within a map, array, or struct) are also schema'd. If this validation passed,
it would make null function as top-type, and allow non-schema'd data embedded
inside of schema'd data.
> Flatten SMT throws NPE
> ----------------------
>
> Key: KAFKA-16858
> URL: https://issues.apache.org/jira/browse/KAFKA-16858
> Project: Kafka
> Issue Type: Bug
> Components: connect
> Affects Versions: 3.6.0
> Environment: Kafka 3.6 by way of CP 7.6.0
> Reporter: Adam Strickland
> Priority: Major
> Attachments: FlattenTest.java
>
>
> {{ConnectSchema.expectedClassesFor}} sometimes will throw an NPE as part of a
> call to an SMT chain. Stack trace snippet:
> {{at
> com.github.momenttechnology.kafka.connect.transforms.MomentFlatten.apply(MomentFlatten.java:84)}}
> {{at
> com.github.momenttechnology.kafka.connect.transforms.MomentFlatten.applyWithSchema(MomentFlatten.java:173)}}
> {{at
> com.github.momenttechnology.kafka.connect.transforms.MomentFlatten.buildWithSchema(MomentFlatten.java:280)}}
> {{at
> com.github.momenttechnology.kafka.connect.transforms.MomentFlatten.buildWithSchema(MomentFlatten.java:280)}}
> {{at
> com.github.momenttechnology.kafka.connect.transforms.MomentFlatten.buildWithSchema(MomentFlatten.java:280)}}
> {{at
> com.github.momenttechnology.kafka.connect.transforms.MomentFlatten.buildWithSchema(MomentFlatten.java:274)}}
> {{at org.apache.kafka.connect.data.Struct.put(Struct.java:203)}}
> {{at org.apache.kafka.connect.data.Struct.put(Struct.java:216)}}
> {{at
> org.apache.kafka.connect.data.ConnectSchema.validateValue(ConnectSchema.java:255)}}
> {{at
> org.apache.kafka.connect.data.ConnectSchema.validateValue(ConnectSchema.java:213)}}
> {{at
> org.apache.kafka.connect.data.ConnectSchema.validateValue(ConnectSchema.java:224)}}
> {{at
> org.apache.kafka.connect.data.ConnectSchema.expectedClassesFor(ConnectSchema.java:268)}}
> (the above transform is a sub-class of
> {{{}o.a.k.connect.transforms.Flatten{}}}; have confirmed that the error
> occurs regardless).
> The field being transformed is an array of structs. If the call to
> {{Schema#valueSchema()}} (o.a.k.connect.data.ConnectSchema.java:255) returns
> {{{}null{}}}, the subsequent call to {{Schema#name()}} at
> o.a.k.connect.data.ConnectSchema:268 throws an NPE.
> The strange thing that we have observed is that this doesn't always happen;
> *sometimes* the struct's schema is found and sometimes it is not. We have
> been unable to determine the root cause, but have constructed a test that
> replicates the problem as observed (see attachment).
> In our case we have worked around the issue with the aforementioned sub-class
> of {{{}Flatten{}}}, catching and logging the NPE on that specific use-case.
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