What I discovered, when playing around with Multiverse is what was actually happening when you use slots on separate worlds, at any given time, the server only loads
one world at server restart time, so what is required of AnCasino is that the the other worlds need to be preloaded to not to be considered "null" when the slots themselves get loaded into the server, that's what this change does:
The last update (v1.4.1.2) is now redundant, as this update (v1.4.2) should now be working and you shouldn't be getting those errors anymore. And
don't worry, this line of code will not delete your worlds, what it does is it checks if the world exists and if it doesn't it creates a new world to put those slots in, and it loads it regardless.
I actually tested this before releasing this as I don't want people's servers getting deleted unintentionally. If you want those weird situations where you want a fresh world with the slots in the same location (which I don't know why you would want that lol), when you find the location of the slot machine, MAKE sure the controller (the button you press to "roll it") is a note block, if it's not use world edit to change it into one, and then the slot will behave as it was created with commands.
Note: This loads EVERY world that each slot machine is in at the start of the server, use /casino reload from now on, DON'T reload the server.