code: @Override
      public boolean isValidUser(String userSecurityName) throws RegistryException {
          if (userSecurityName == null) {
              throw new IllegalArgumentException("userSecurityName is null");
          }
          String userName = userSecurityName.trim();
          if (userName.isEmpty()) {
              throw new IllegalArgumentException("userSecurityName is an empty String");
          }
          if (state.ignoreCaseForAuthentication) {
              for (Map.Entry<String, BasicPassword> entry : state.users.entrySet()) {
                  String keyUserName = entry.getKey();
                  if (keyUserName.equalsIgnoreCase(userSecurityName)) {
                      return true;
                  }
              }
              return false;
          }
          return state.users.containsKey(userName);
      }
docs: {@inheritDoc}