@NotNull
  private static String getDigitPrefix(@NotNull String indexName) {
    int i;
    for (i = 0; i < indexName.length(); i++) {
      final char c = indexName.charAt(i);
      if (!Character.isDigit(c)) {
        break;
      }
    }
    return i == 0 ? "" : indexName.substring(0, i);
  }
@NotNull
  private static String getDigitPrefix(@NotNull String indexName)