That’s why my original fileinfo pattern is
/lost+found/*
/lost+found/.
and for an empty folder, this shows up in the 1.5 agent output as:
/lost+found/*|missing|1623420168
/lost+found/.|16384|1563346155
On the Checmk server, I then group all “/lost+found/*” paths and ignore the directory (“.”) itself. This gives a check for the file group which then can go WARN or CRIT when the count is > 0.
Or at least that’s how I did it in 1.5 
So, probably time to brush up my miserable perl skills … or hope that some expert (or tribe29 even) can have a look 
Thanks
Martin