Server tick loop error 1.12.2

[ModdMeMaybe18]

I keep getting this error every time I load Minecraft and click on a world. I am developing a mod and I get this error:

 

[10:51:08] [Server thread/INFO] [FML]: The state engine was in incorrect state SERVER_STARTING and forced into state SERVER_STOPPED. Errors may have been discarded.
[10:51:09] [Client thread/INFO] [STDOUT]: [net.minecraft.init.Bootstrap:printToSYSOUT:629]: ---- Minecraft Crash Report ----
// I let you down. Sorry

Time: 7/21/19 10:51 AM
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
    at net.minecraft.village.VillageCollection.fileNameForProvider(VillageCollection.java:321)
    at net.minecraft.world.WorldServerMulti.init(WorldServerMulti.java:68)
    at net.minecraft.server.integrated.IntegratedServer.loadAllWorlds(IntegratedServer.java:127)
    at net.minecraft.server.integrated.IntegratedServer.init(IntegratedServer.java:160)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:552)
    at java.lang.Thread.run(Unknown Source)