@Override
    public void stop() {
        if (executor != null) {
            ThreadUtils.shutdownExecutorServiceQuietly(executor, 30, TimeUnit.SECONDS);
            executor = null;
        }
    }
Implementation of OffsetBackingStore that doesn't actually persist any data. To ensure this
behaves similarly to a real backing store, operations are executed asynchronously on a
background thread.
connect/runtime/src/main/java/org/apache/kafka/connect/storage/MemoryOffsetBackingStore.java