docs: private void validateFields(List<String> fields) {
          if (fields == null) {
              return;
          }
          List<String> badFields = new ArrayList<String>();
          for (String field: fields) {
              if (field.contains(".")) {
                  badFields.add(field);
              }
          }
  
          if (!badFields.isEmpty()) {
              String msg = String.format("Projection field(s) cannot use dotted notation: %s",
                      Misc.join(", ", badFields));
              logger.log(Level.SEVERE, msg);
              throw new IllegalArgumentException(msg);
          }
      }