code: @Override
      public String getUserDisplayName(String userSecurityName) throws EntryNotFoundException, RegistryException {
          if (userSecurityName == null) {
              throw new IllegalArgumentException("userSecurityName is null");
          }
          if (userSecurityName.isEmpty()) {
              throw new IllegalArgumentException("userSecurityName is an empty String");
          }
  
          if (!isValidUser(userSecurityName)) {
              throw new EntryNotFoundException(userSecurityName + " does not exist");
          }
          return userSecurityName;
      }
docs: {@inheritDoc}