docs: @Nonnull
    public EChange setSystemMessage (@Nonnull final ESystemMessageType eMessageType, @Nullable final String sMessage)
    {
      ValueEnforcer.notNull (eMessageType, "MessageType");
  
      if (m_eMessageType.equals (eMessageType) && EqualsHelper.equals (m_sMessage, sMessage))
        return EChange.UNCHANGED;
  
      internalSetMessageType (eMessageType);
      internalSetMessage (sMessage);
      setLastUpdate (PDTFactory.getCurrentLocalDateTime ());
  
      return EChange.CHANGED;
    }