Some one can tell me why i get this error code some times?
Java:
25.07 14:25:45 [Server] WARN java.util.concurrent.ExecutionException: java.lang.NullPointerException
25.07 14:25:45 [Server] WARN at java.util.concurrent.FutureTask.report(FutureTask.java:122)
25.07 14:25:45 [Server] WARN at java.util.concurrent.FutureTask.get(FutureTask.java:192)
25.07 14:25:45 [Server] WARN at com.w00tmast3r.skquery.elements.effects.EffOptionThread$1.run(EffOptionThread.java:43)
25.07 14:25:45 [Server] WARN at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:71)
25.07 14:25:45 [Server] WARN at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:350)
25.07 14:25:45 [Server] WARN at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:723)
25.07 14:25:45 [Server] WARN at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374)
25.07 14:25:45 [Server] WARN at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654)
25.07 14:25:45 [Server] WARN at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557)
25.07 14:25:45 [Server] WARN at java.lang.Thread.run(Thread.java:745)
25.07 14:25:45 [Server] WARN Caused by: java.lang.NullPointerException
25.07 14:25:45 [Server] WARN at sun.reflect.GeneratedMethodAccessor186.invoke(Unknown Source)
25.07 14:25:45 [Server] WARN at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
25.07 14:25:45 [Server] WARN at java.lang.reflect.Method.invoke(Method.java:498)
25.07 14:25:45 [Server] WARN at com.w00tmast3r.skquery.elements.effects.EffOptionThread$2.call(EffOptionThread.java:61)
25.07 14:25:45 [Server] WARN at com.w00tmast3r.skquery.elements.effects.EffOptionThread$2.call(EffOptionThread.java:58)
25.07 14:25:45 [Server] WARN at java.util.concurrent.FutureTask.run(FutureTask.java:266)
25.07 14:25:45 [Server] WARN at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
25.07 14:25:45 [Server] WARN at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)