default void deleteAll(List<K> keys) {
    for (K key : keys) {
      delete(key);
    }
  }
Deletes the mappings for the specified {@code keys} from this key-value store (if such mappings exist).

@param keys the keys for which the mappings are to be deleted.
@throws NullPointerException if the specified {@code keys} list, or any of the keys, is {@code null}.
samza-api/src/main/java/org/apache/samza/storage/kv/KeyValueStore.java