1. Go to the editor, place a player unit (eg BLUFOR rifleman), place a trigger activated by radio. Activation field for this trigger:
player unlinkItem "";
2. Save scenario;
3. Exit the game;
4. Launch the game again;
5. Go to the editor;
6. Load saved scenario;
7. Activate the trigger.
As the result is config error message on screen followed by RPT log. Second try will generate no errors, but if you put there some fictional class instead of "", eg "xxx", you'll get it one time again; etc. for any new invalid classname. If class is valid (refers to an item actually existing in the config), but unit hasn't this item assigned - error not occurs.