private Iterable<DataNodeConfig> lazyIterable(Collection<ZNRecord> records) {
      return records == null || records.isEmpty() ? Collections.emptyList()
          : () -> records.stream().filter(Objects::nonNull).map(converter::convert).filter(Objects::nonNull).iterator();
    }
Tell the background executor to perform any initialization needed. This should be called after registering this
listener using {@link HelixPropertyStore#subscribe}. This will ensure that the first event sent to
{@link #listener} will contain the entire set of current configs.
@throws Exception if there was an exception while making the initialization call.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/PropertyStoreToDataNodeConfigAdapter.java