docs: public static boolean isIdOrFullnameAllowed(@CheckForNull String id) {
          if (StringUtils.isBlank(id)) {
              return false;
          }
          final String trimmedId = id.trim();
          for (String invalidId : ILLEGAL_PERSISTED_USERNAMES) {
              if (trimmedId.equalsIgnoreCase(invalidId))
                  return false;
          }
          return true;
      }