@Override
    public void start() {
        // Worker offset store should already be started
        connectorStore.ifPresent(OffsetBackingStore::start);
    }
If configured to use a connector-specific offset store, {@link OffsetBackingStore#start() start} that store.

<p>The worker-global offset store is not modified; it is the caller's responsibility to ensure that it is started
before calls to {@link #get(Collection)} and {@link #set(Map, Callback)} take place.
connect/runtime/src/main/java/org/apache/kafka/connect/storage/ConnectorOffsetBackingStore.java