Federico Valeri created KAFKA-20020:
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Summary: Improve UUID nullability description in API readme
Key: KAFKA-20020
URL: https://issues.apache.org/jira/browse/KAFKA-20020
Project: Kafka
Issue Type: Bug
Components: documentation
Affects Versions: 4.1.1
Reporter: Federico Valeri
The Nullable Fields section in the Kafka message protocol readme can make
people think that they can declare nullable a field of type Uuid:
{code}
Booleans, ints, and floats can never be null. However, fields that are strings,
bytes, uuid, records, or arrays may optionally be "nullable". When a field is
"nullable", that simply means that we are prepared to serialize and deserialize
null entries for that field.
...
If a field is declared as non-nullable, and it is present in the message
version you are using, you should set it to a non-null value before serializing
the message. Otherwise, you will get a runtime error.
{code}
This is not possible by design as the UUIDFieldType class does NOT override
canBeNullable(), so it inherits the default implementation which returns false.
Uuid fields use a special zero uuid value (all bits set to 0) as a sentinel to
represent "no UUID" instead of null.
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