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https://issues.apache.org/jira/browse/AVRO-1482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13935517#comment-13935517
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Sean Busbey commented on AVRO-1482:
-----------------------------------
+1 looks good to me.
> in specification, put "null" first in unions
> --------------------------------------------
>
> Key: AVRO-1482
> URL: https://issues.apache.org/jira/browse/AVRO-1482
> Project: Avro
> Issue Type: Improvement
> Components: doc
> Reporter: Doug Cutting
> Fix For: 1.7.7
>
> Attachments: AVRO-1482.patch
>
>
> Unions with null are a common schema idiom. When a default-value is
> specified, it is most often null. Default values for unions must be of the
> type of the first element in the union. So normally, when specifying a union
> with null, one places the null first so that one can use null as the default
> value. Folks often make the mistake of specifying null as the default value
> when it is not the first value in the union. Thus the best practice is to
> put null as the first element when it is in a union unless you specify a
> non-null default value.
> Several example schemas in the specification do not put the null first in the
> union schema. The specification should set a better example, to help folks
> to avoid this potential confusion. It might also mention this issue more
> explicitly.
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