@Override
  public Map<K, V> getAll(List<K> keys) {
    Map<K, V> values = new HashMap<>();
    for (K key : keys) {
      values.put(key, map.get(key));
    }
    return values;
  }
Implements a {@link KeyValueStore} using an in-memory Java Map.
@param <K>  the type of key
@param <V>  the type of value

TODO: This class is a stop-gap until we implement persistent store creation from TaskContext.
samza-core/src/main/java/org/apache/samza/operators/util/InternalInMemoryStore.java