When trying to place another slab on top of any slab from midnight the game will give the following crash:
https://paste.dimdev.org/urofubekaw.mccrash
I've blacklisted all of midnight's slabs and even tried to disable "Replace Same Slab". My blacklist looks like:
S:"Slab Blacklist" <
midnight:shadowroot_slab
midnight:dead_wood_slab
midnight:dark_willow_slab
midnight:nightstone_slab
midnight:nightstone_brick_slab
midnight:trenchstone_slab
midnight:trenchstone_brick_slab
midnight:dewshroom_slab
midnight:viridshroom_slab
midnight:nightshroom_slab
midnight:rockshroom_bricks_slab
>

and here's the code relevant to the crash:
getVariantProperty() code

I see that the method is being called here: DoubleSlabsConfig.java#L37
Which I'm guessing is the cause of the crash, seeing as it is always run regardless of blacklisting (at least, that's my guess I don't know the full implementation). Is there a way to make a workaround for this?

This should be fixed in the latest version! Thanks for the report!