private RecordAccumulator createTestRecordAccumulator(int deliveryTimeoutMs, int batchSize, long totalSize, Compression compression, int lingerMs) {
        return createTestRecordAccumulator(null, deliveryTimeoutMs, batchSize, totalSize, compression, lingerMs);
    }
Return the offset delta when there is no key.
clients/src/test/java/org/apache/kafka/clients/producer/internals/RecordAccumulatorTest.java