The user can be informed about anything strange happened during the execution of the node with this method. This will not cancel execution but set a warning icon with the provided message as the tooltip.
Example #1:
if (m_includedColumns.getIncludeList() == null || m_includedColumns.getIncludeList().size() <= 0) { setWarningMessage( "No columns to transfrom selected. Will have no effect!"); }