[11:26:00 WARN]: [Practice] Task #257 for Practice v1.0 generated an exception
java.lang.NullPointerException
        at practice.utils.Duel.lambda$null$19(Duel.java:732) ~[?:?]
        at practice.utils.Duel.forEveryone(Duel.java:448) ~[?:?]
        at practice.utils.Duel.lambda$close$21(Duel.java:718) ~[?:?]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:59) ~[nspigot-2.0E.jar:1.8.8]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:344) ~[nspigot-2.0E.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:761) ~[nspigot-2.0E.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:342) ~[nspigot-2.0E.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:710) ~[nspigot-2.0E.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.MinecraftServer.lambda$startTickloop$0(MinecraftServer.java:599) ~[nspigot-2.0E.jar:1.8.8]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_191]
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [?:1.8.0_191]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_191]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [?:1.8.0_191]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_191]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_191]