org.apache.kafka.common.serialization.Deserializer is missing Nullable declaration

[snicoll]

In what version(s) of Spring for Apache Kafka are you seeing this issue?

main

Describe the bug

org.apache.kafka.common.serialization.Deserializer has several deserialization methods that are documented as:

• @return deserialized typed data; may be null

However these methods are not marked as @Nullable. This has a knock-off effect in RetryingDeserializer as well.