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https://issues.apache.org/jira/browse/KAFKA-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17311954#comment-17311954
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A. Sophie Blee-Goldman commented on KAFKA-9559:
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I don't think we can just throw an exception based on whether `defaultKeySerde`
is null, as we _always_ pass this in to initialize the keySerde in
AbstractProcessorContext. Then we have about a million (ok, like 30) places
where we call AbstractProcessorContext#key/valueSerde to get the default, and
then maybe do/don't actually use that default serde by checking whether the
operator/whatever has configured a specific serde. So we couldn't just throw an
exception on null inside StreamsConfig#defaultKey/ValueSerde, and we can't
throw if null inside AbstractProcessorContext#key/valueSerde without doing some
refactoring of the downstream logic. For example see how things get passed
through WrappingNullableUtils#prepareSerde(specificSerde, contextkeySerde,
contextValueSerde)
So, it's possible but it just might involve more work. Maybe not "Everywhere
serdes are used" painful, though
> Change the default "default serde" from ByteArraySerde to null
> --------------------------------------------------------------
>
> Key: KAFKA-9559
> URL: https://issues.apache.org/jira/browse/KAFKA-9559
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: A. Sophie Blee-Goldman
> Assignee: Leah Thomas
> Priority: Blocker
> Fix For: 3.0.0
>
>
> The current default "default serde" is not particularly useful, and in almost
> all cases is intended to be overwritten either by setting the config
> explicitly or by specifying serdes directly in the topology. If a user does
> not set the config and misses specifying a serde they will get a runtime
> ClassCastException once they start processing unless they are in fact
> processing only bytes.
> We should change the default default to null, so that an exception will
> instead be thrown immediately on startup if a user failed to specify a serde
> somewhere in their topology and it falls back to the unset default.
>
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