[15:54:35 FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_111]
at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_111]
at net.minecraft.server.v1_11_R1.SystemUtils.a(SourceFile:47) [server.jar:git-Spigot-16c940b-88eede8]
at net.minecraft.server.v1_11_R1.MinecraftServer.D(MinecraftServer.java:739) [server.jar:git-Spigot-16c940b-88eede8]    at net.minecraft.server.v1_11_R1.DedicatedServer.D(DedicatedServer.java:399) [server.jar:git-Spigot-16c940b-88eede8]    at net.minecraft.server.v1_11_R1.MinecraftServer.C(MinecraftServer.java:675) [server.jar:git-Spigot-16c940b-88eede8]    at net.minecraft.server.v1_11_R1.MinecraftServer.run(MinecraftServer.java:574) [server.jar:git-Spigot-16c940b-88eede8]  at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]Caused by: java.lang.NullPointerException at net.minecraft.server.v1_11_R1.PacketPlayOutSetSlot.<init>(SourceFile:25) ~[server.jar:git-Spigot-16c940b-88eede8]    at net.minecraft.server.v1_11_R1.PlayerConnection.a(PlayerConnection.java:1999) ~[server.jar:git-Spigot-16c940b-88eede8]
    at net.minecraft.server.v1_11_R1.PacketPlayInSetCreativeSlot.a(SourceFile:23) ~[server.jar:git-Spigot-16c940b-88eede8]  at net.minecraft.server.v1_11_R1.PacketPlayInSetCreativeSlot.a(SourceFile:9) ~[server.jar:git-Spigot-16c940b-88eede8]   at net.minecraft.server.v1_11_R1.PlayerConnectionUtils$1.run(SourceFile:13) ~[server.jar:git-Spigot-16c940b-88eede8]    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_111]   at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_111]  at net.minecraft.server.v1_11_R1.SystemUtils.a(SourceFile:46) ~[server.jar:git-Spigot-16c940b-88eede8]  ... 5 more