The error suggests the code is expecting at least one modifier.
Here is hopefully a tweak that checks if there are any modifiers before trying to access the first one:
MeshSplit1.1.1.zip (1.8 KB)
Do bear in mind that it’s been a few years since I wrote that, and it was written for v2.79, which I’m not using since 2.8x is the current version, so I haven’t tested it and there might be something I’ve overlooked. In other words, cross your fingers before running it.