AVRO-4211: Java Schema Gen for Unions w/ Default Value

[zakpayne8283]

What is the purpose of the change

This PR addresses AVRO-4211. In Java, the IDLUtils does not generate Schemas correctly for fields which are unions and have a default value if the default value is not the first element in the union.

For example:

@Union({ Void.class, Integer.class })
@AvroDefault("1")
int someIntField = 1

Will produce a Schema like

someIntField = null

because Void.class is the first element in the union.

This change aligns the Java library with the current documentation:

Note that when a default value is specified for a record field whose type is a union, the type of the default value must match with one element of the union.

Verifying this change

This change modified tests and can be verified as follows:

Modified TestJacksonUtils.java, adding a union with default value matching the second element of the union to the testToObject() test.

Documentation

• Does this pull request introduce a new feature?
  • No