I’m working with Apache Flink’s Python API (PyFlink) and trying to implement custom serialization for the keys in a Kafka producer. My goal is to modify the keys before sending them to a Kafka topic using a custom serialization schema. However, I’m encountering a NullPointerException when trying to use my custom serialization schema in the KafkaSink setup. I am unsure if my approach to implementing the custom serialization is correct or if there is a limitation with PyFlink’s support for custom serializers. Here’s the code snippet I’m working with:
`
from pyflink.common.serialization import SerializationSchema

class CustomKeySerializationSchema(SerializationSchema):
def serialize(self, value):
# Example modification to the key before serialization
try:
modified_value = value + “_custom”
return modified_value.encode(‘utf-8’)
except Exception as e:
print(“Error during serialization:”, e)
return None

kafka_producer = KafkaSink.builder()
.set_bootstrap_servers(“localhost:9092”)
.set_record_serializer(
KafkaRecordSerializationSchema.builder()
.set_topic_selector(lambda element: “DIJ.test”)
.set_key_serialization_schema(CustomKeySerializationSchema())
.set_value_serialization_schema(CustomKeySerializationSchema())
.build()
)
.build()
`

Questions:

1. Is there a known limitation or issue in PyFlink that prevents the use of custom serialization schemas for keys in KafkaSink?
2. How can I properly implement custom serialization for keys in PyFlink without encountering a NullPointerException?
3. Are there alternative approaches to achieve custom key serialization in a Kafka producer using PyFlink?
4. Any guidance or suggestions would be greatly appreciated, as I am unable to find much documentation on custom serializers in the PyFlink context.

I tried reading the source code and documentation. Both were unhelpful.