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https://issues.apache.org/jira/browse/KAFKA-16858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17850173#comment-17850173
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Greg Harris commented on KAFKA-16858:
-------------------------------------
It really confused me that the stacktrace is in reverse order, is there a tool
that does that by default?
I confirmed that ConnectSchema.validateValue() throws NPE when given a null
schema, this is replicated with this assertion:
{noformat}
assertThrows(NullPointerException.class, () ->
ConnectSchema.validateValue(null, new Object()));
{noformat}
I can also confirm that this NPE appears when using
SchemaBuilder.arrayOfNull(), which would cause `valueSchema()` to return null.
The exception only appears when the array is non-empty.
{noformat}
final String fieldName = "fieldName";
Schema testSchema = SchemaBuilder.struct()
.field(fieldName, SchemaBuilder.arrayOfNull());
new Struct(testSchema).put(fieldName, Collections.emptyList());
assertThrows(NullPointerException.class, () ->
new Struct(testSchema).put(fieldName, Collections.singletonList(new
Object())));
{noformat}
Looking at the way Flatten works, it's just copying schemas from input to
output, so an arrayOfNull() can appear if the input contained an arrayOfNull():
[https://github.com/apache/kafka/blob/4d04eb83ea2cf67484d81e30603e976f63616428/connect/transforms/src/main/java/org/apache/kafka/connect/transforms/util/SchemaUtil.java#L29]
Since this is a type that SchemaBuilder can emit, we should probably handle it
intentionally, either emitting a DataException, or passing the validation.
[~undone] For my own reference: Do you see this fault with another SMT in the
chain ahead of Flatten? What Converter implementation are you using? There's
also a very noisy log statement you could use to figure out where this
null-array-schema is appearing:
[https://github.com/apache/kafka/blob/4d04eb83ea2cf67484d81e30603e976f63616428/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/TransformationChain.java#L53]
> 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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