Problem/Bug Server crashes as soon as anyone joins

I just started the server and then i tried joining in but it crashed and the console closed itself
Here is the log, on the part of the error
I also tried getting some of my friends to join but the same thing happened

Encountered an unexpected exception
java.lang.ArrayIndexOutOfBoundsException: 16
at net.minecraft.server.v1_12_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:384) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at net.minecraft.server.v1_12_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:87) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at net.minecraft.server.v1_12_R1.ChunkRegionLoader.loadChunk(ChunkRegionLoader.java:65) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at org.bukkit.craftbukkit.v1_12_R1.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:21) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at org.bukkit.craftbukkit.v1_12_R1.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:1) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor$Task.init(AsynchronousExecutor.java:150) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor$Task.initAsync(AsynchronousExecutor.java:95) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor$Task.run(AsynchronousExecutor.java:85) ~[craftbukkit-1.12.2.jar:git-Bukkit-dc7d31b]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) ~[?:1.8.0_151]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) ~[?:1.8.0_151]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_151]