@Override
    public void register(final StateStore store,
                         final StateRestoreCallback stateRestoreCallbackIsIgnoredInMock) {
        stateStores.put(store.name(), store);
    }
Returns the headers of the current input record; could be {@code null} if it is not
available.

<p> Note, that headers should never be {@code null} in the actual Kafka Streams runtime,
even if they could be empty. However, this mock does not guarantee non-{@code null} headers.
Thus, you either need to add a {@code null} check to your production code to use this mock
for testing or you always need to set headers manually via {@link #setHeaders(Headers)} to
avoid a {@link NullPointerException} from your {@link Processor} implementation.

@return the headers
streams/test-utils/src/main/java/org/apache/kafka/streams/processor/MockProcessorContext.java