@Override
  public void delete(String namespacedKey) {
    // Since kafka doesn't support individual message deletion, store value as null for a namespacedKey to delete.
    put(namespacedKey, null);
  }
An implementation of the {@link MetadataStore} interface where the metadata of the samza job is stored in coordinator stream.

This class is thread safe.

It is recommended to use {@link NamespaceAwareCoordinatorStreamStore}. This will enable the single CoordinatorStreamStore connection
to be shared by the multiple {@link NamespaceAwareCoordinatorStreamStore} instances.
samza-core/src/main/java/org/apache/samza/coordinator/metadatastore/CoordinatorStreamStore.java