code: private void validateNamesUnique(List<String> names) {
      List<String> seenNames = new ArrayList<>(names.size());
      for (int i = 0; i < names.size(); i++) {
        String lowerCaseName = names.get(i).toLowerCase();
        int index = seenNames.indexOf(lowerCaseName);
        if (index != -1) {
          throw new IllegalArgumentException("Duplicate field: " + lowerCaseName + " found at positions " + i + "and"
              + index + ". Field names are case insensitive and must be unique.");
        }
        seenNames.add(lowerCaseName);
      }
    }
docs: For full ORC compatibility, field names should be unique when lowercased.