[jira] [Created] (AVRO-4273) The type of the default value must match with one element of the union

["Cédric Jäger (Jira)" <ji...@apache.org>]

Cédric Jäger created AVRO-4273:
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             Summary: The type of the default value must match with one element of the union
                 Key: AVRO-4273
                 URL: https://issues.apache.org/jira/browse/AVRO-4273
             Project: Apache Avro
          Issue Type: Bug
          Components: java
    Affects Versions: 1.12.1
            Reporter: Cédric Jäger
             Fix For: 1.12.2


The actual specification for [unions|https://avro.apache.org/docs/++version++/specification/#unions] states : "the type of the default value must match with *one* element of the union"

The actual implementation of the GenericData class on [line 1338|https://github.com/apache/avro/blob/840dc8139f4b3d1bfa8e8c8f1ac3be949b440634/lang/java/avro/src/main/java/org/apache/avro/generic/GenericData.java#L1338], however, checks only for the first element of the union :
{code:java}
    if (json.isNull() && (field.schema().getType() == Type.NULL
        || (field.schema().getType() == Type.UNION && field.schema().getTypes().get(0).getType() == Type.NULL))) {
      return null;
    } {code}
This causes a problem when there is a nullable field with a default value of null and null is not defined as the first element of the union in the schema :

Instead, the code should iterate through the elements of the union to check if one of them is of type NULL, and return null if it is.



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