Bug: ConsumerRecordRecords.key returns None when record key is an empty string #8696

Expected Behaviour

When a Kafka event contains an empty key ("key": ""), ConsumerRecordRecords.key should deserialize the empty string and return an empty key (e.g. "" or b""), matching Kafka semantics and KafkaEventRecord.decoded_key behavior. Only missing or null keys (None) should evaluate to None.

Current Behaviour

In aws_lambda_powertools/utilities/kafka/consumer_records.py (line 35):

key = self.get("key")

# Return None if key doesn't exist
if not key:
    return None

Because if not key: performs a truthiness check rather than an identity check against None, any empty base64 string ("key": "") is treated as nonexistent and returns None.

In contrast, KafkaEventRecord.decoded_key in aws_lambda_powertools.utilities.data_classes.kafka_event correctly distinguishes between missing and empty keys:

return None if self.key is None else base64.b64decode(self.key)

Code snippet

from aws_lambda_powertools.utilities.kafka.consumer_records import ConsumerRecordRecords

data = {
    "topic": "test-topic",
    "partition": 0,
    "offset": 100,
    "timestamp": 1690000000000,
    "timestampType": "CREATE_TIME",
    "key": "",  # Empty key representation in Kafka event
    "value": "dGVzdC12YWx1ZQ==",
}

record = ConsumerRecordRecords(data=data)

# Fails: returns None instead of empty decoded key
assert record.key is not None

Possible Solution

Update line 35 of aws_lambda_powertools/utilities/kafka/consumer_records.py:

-        if not key:
+        if key is None:
             return None

And add unit regression tests verifying empty string key handling.

Steps to Reproduce

1. Instantiate ConsumerRecordRecords with a dict containing "key": "".
2. Access record.key.
3. Observe it returns None instead of deserializing the empty key.

Powertools for AWS Lambda (Python) version

latest

AWS Lambda function runtime

3.12

Packaging format used

PyPi