[23:18:38 ERROR]: Encountered an unexpected exception
java.lang.NoClassDefFoundError: java/util/concurrent/ForkJoinTask
        at it.unimi.dsi.fastutil.longs.LongArraySet.<init>(LongArraySet.java:99) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.ChunkProviderServer.<init>(ChunkProviderServer.java:26) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.WorldServer.n(WorldServer.java:845) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.WorldServer.<init>(WorldServer.java:66) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.MinecraftServer.a(MinecraftServer.java:273) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.DedicatedServer.init(DedicatedServer.java:268) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.MinecraftServer.run(MinecraftServer.java:532) [spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at java.lang.Thread.run(Thread.java:701) [?:1.6.0_38]
Caused by: java.lang.ClassNotFoundException: java.util.concurrent.ForkJoinTask
        at java.net.URLClassLoader$1.run(URLClassLoader.java:217) ~[?:1.6.0_38]
        at java.security.AccessController.doPrivileged(Native Method) ~[?:1.6.0_38]
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205) ~[?:1.6.0_38]
        at java.lang.ClassLoader.loadClass(ClassLoader.java:323) ~[?:1.6.0_38]
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294) ~[?:1.6.0_38]
        at java.lang.ClassLoader.loadClass(ClassLoader.java:268) ~[?:1.6.0_38]
        ... 8 more
[23:18:38 ERROR]:       Cause of unexpected exception was
java.lang.ClassNotFoundException: java.util.concurrent.ForkJoinTask
        at java.net.URLClassLoader$1.run(URLClassLoader.java:217) ~[?:1.6.0_38]
        at java.security.AccessController.doPrivileged(Native Method) ~[?:1.6.0_38]
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205) ~[?:1.6.0_38]
        at java.lang.ClassLoader.loadClass(ClassLoader.java:323) ~[?:1.6.0_38]
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294) ~[?:1.6.0_38]
        at java.lang.ClassLoader.loadClass(ClassLoader.java:268) ~[?:1.6.0_38]
        at it.unimi.dsi.fastutil.longs.LongArraySet.<init>(LongArraySet.java:99) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.ChunkProviderServer.<init>(ChunkProviderServer.java:26) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.WorldServer.n(WorldServer.java:845) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.WorldServer.<init>(WorldServer.java:66) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.MinecraftServer.a(MinecraftServer.java:273) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.DedicatedServer.init(DedicatedServer.java:268) ~[spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at net.minecraft.server.v1_9_R2.MinecraftServer.run(MinecraftServer.java:532) [spigot-1.9.4.jar:git-Spigot-4af49dc-e22506f]
        at java.lang.Thread.run(Thread.java:701) [?:1.6.0_38]