ProducerIdAndEpoch producerIdAndEpoch() {
        return producerIdAndEpoch;
    }
Get the current producer id and epoch without blocking. Callers must use {@link ProducerIdAndEpoch#isValid()} to
verify that the result is valid.

@return the current ProducerIdAndEpoch.
clients/src/main/java/org/apache/kafka/clients/producer/internals/TransactionManager.java