default Map<K, V> getAll(List<K> keys) {
    Map<K, V> map = new HashMap<>(keys.size());

    for (K key : keys) {
      V value = get(key);

      if (value != null) {
        map.put(key, value);
      }
    }

    return map;
  }
Gets the values with which the specified {@code keys} are associated.

@param keys the keys with which the associated values are to be fetched.
@return a map of the keys that were found and their respective values.
@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