@NotNull
  @Override
  @Internal
  public <K, V> UpdatableIndex<K, V, FileContent, ?> getIndex(ID<K, V> indexId) {
    UpdatableIndex<K, V, FileContent, ?> index = getState().getIndex(indexId);
    if (index == null) {
      Throwable initializationProblem = getState().getInitializationProblem(indexId);
      String message = "Index is not created for `" + indexId.getName() + "`";
      throw initializationProblem != null
            ? new IllegalStateException(message, initializationProblem)
            : new IllegalStateException(message);
    }
    return index;
  }
@NotNull
  @Override
  @Internal
  public <K, V> UpdatableIndex<K, V, FileContent, ?> getIndex(ID<K, V> indexId)