There goes the only use there ever was for MZ (and MV, actually).
You shouldn't have to use an actual picture, literally a blank file without any data in it with that filename should do the trick, but honestly, all that bloated nwjs crap is supposed to perform a full run on boot, not when you change maps...
(If you do try this and it doesn't work, then just use the smallest possible valid file format accepted by RMMV/RMMZ. It's recommended to keep all of these the same size to easily find the placeholders, though using touch - or whatever way you feel like using - to modify the timestamp would also work as RM - fortunately - does not write to asset files, it only reads from them.)
So much for dropping the RTP "just so people don't encounter missing files". If files are not included and you fail to perform a full check on boot (this doesn't take aeons if you're doing it right, it takes literal seconds unless you're also calculating checksums and whatnot, then might want to inform the player it'll only be done ONCE*) shit will happen...
Sorry for the unnecessary RPG Maker rant but seriously...
*excluding when data is modified
**and another failed stealth edit, I'm way too slow
tl;dr: Add either one in /img/pictures/
