docs: protected static boolean validFieldName(String fieldName) {
          String[] parts = fieldName.split("\\.");
          for (String part: parts) {
              if (part.startsWith("$")) {
                  String msg = String.format("Field names cannot start with a $ in field %s", part);
                  logger.log(Level.SEVERE, msg);
                  return false;
              }
          }
  
          return true;
      }