Doug Cutting created AVRO-1482:
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Summary: 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
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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