code: @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;
    }
docs: Set the system message type and text, and update the last modification
  date.
  
  @param eMessageType
  Message type. May not be <code>null</code>.
  @param sMessage
  The message text. May be <code>null</code>.
  @return {@link EChange}