[07:34:54] [Server thread/FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: -999
at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_66]
at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_66]
at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:45) [spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:715) [spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374) [spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) [spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557) [spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_66]
Caused by: java.lang.ArrayIndexOutOfBoundsException: -999
at java.util.ArrayList.elementData(ArrayList.java:418) ~[?:1.8.0_66]
at java.util.ArrayList.get(ArrayList.java:431) ~[?:1.8.0_66]
at net.minecraft.server.v1_8_R3.Container.clickItem(Container.java:141) ~[spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:1595) ~[spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.PacketPlayInWindowClick.a(SourceFile:31) ~[spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.PacketPlayInWindowClick.a(SourceFile:9) ~[spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) ~[spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_66]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_66]
at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) ~[spigot-1.8.8.jar:git-Spigot-db6de12-3f3c65f]
... 5 more