I changed a few lines and did /reload in a single player world and it crashed, When I looked in the function I instantly saw that I had a line with improper syntax and it seems as this is what caused the crash..
Note that this is duplicated on https://bugs.mojang.com/browse/MC-125292 but with a different error/stacktrace on it..
If this is still an issue for you in the latest version of Minecraft, please provide the function files.