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https://issues.apache.org/jira/browse/DRILL-7345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16905511#comment-16905511
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Volodymyr Vysotskyi commented on DRILL-7345:
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{quote}
If I were to create an additional UDF which perhaps accepts a NullableVarChar
as an input parameter, and returns null, wouldn't that cause Drill to either
add extra columns or otherwise cause problems?
{quote}
You can create additional UDF which accepts NullableVarChar as an input
parameter and Drill will choose between them both, which one should be used. A
lot of inbuilt UDFs which uses internal nulls handling use this approach.
> Strange Behavior for UDFs with ComplexWriter Output
> ---------------------------------------------------
>
> Key: DRILL-7345
> URL: https://issues.apache.org/jira/browse/DRILL-7345
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.17.0
> Reporter: Charles Givre
> Priority: Minor
>
> I wrote some UDFs recently and noticed some strange behavior when debugging
> them.
> This behavior only occurs when there is ComplexWriter as output.
> Basically, if the input to the UDF is nullable, Drill doesn't recognize the
> UDF at all. I've found that the only way to get Drill to recognize UDFs that
> have ComplexWriters as output is:
> * Use a non-nullable holder as input
> * Remove the null setting completely from the function parameters.
> This approach has a drawback in that if the function receives a null value,
> it will throw an error and halt execution. My preference would be to allow
> null handling, but I've not figured out how to make that happen.
> Note: This behavior ONLY occurs when using a ComplexWriter as output.
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